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 $194.62   13.506%   $220.9054   $220.91   $220.90   $220.90  
  Purchase #2 $220.67   6.843%   $235.7704   $235.77   $235.75   $235.80  
  Purchase #3 $79.99   4.626%   $83.6903   $83.69   $83.70   $83.70  
  Purchase #4 $197.46   8.794%   $214.8246   $214.82   $214.80   $214.80  
  Purchase #5 $117.44   6.644%   $125.2427   $125.24   $125.25   $125.20  
  Purchase #6 $224.99   9.263%   $245.8308   $245.83   $245.85   $245.80  
  Purchase #7 $23.58   7.642%   $25.382   $25.38   $25.40   $25.40  
  7 purchase totals = $1,058.75       $1,151.6462   $1,151.64   $1,151.65   $1,151.60