Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $239.58   10.578%   $264.9228   $264.92   $264.90   $264.90  
  Purchase #2 $170.45   7.734%   $183.6326   $183.63   $183.65   $183.60  
  Purchase #3 $137.32   11.627%   $153.2862   $153.29   $153.30   $153.30  
  Purchase #4 $215.61   8.741%   $234.4565   $234.46   $234.45   $234.50  
  Purchase #5 $243.65   13.867%   $277.4369   $277.44   $277.45   $277.40  
  Purchase #6 $242.26   9.701%   $265.7616   $265.76   $265.75   $265.80  
  Purchase #7 $223.82   9.833%   $245.8282   $245.83   $245.85   $245.80  
  7 purchase totals = $1,472.69       $1,625.3248   $1,625.33   $1,625.35   $1,625.30