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 $53.39   13.820%   $60.7685   $60.77   $60.75   $60.80  
  Purchase #2 $94.69   8.773%   $102.9972   $103.00   $103.00   $103.00  
  Purchase #3 $182.54   8.657%   $198.3425   $198.34   $198.35   $198.30  
  Purchase #4 $237.57   11.309%   $264.4368   $264.44   $264.45   $264.40  
  Purchase #5 $77.49   10.126%   $85.3366   $85.34   $85.35   $85.30  
  Purchase #6 $247.39   10.148%   $272.4951   $272.50   $272.50   $272.50  
  Purchase #7 $121.58   12.853%   $137.2067   $137.21   $137.20   $137.20  
  7 purchase totals = $1,014.65       $1,121.5834   $1,121.60   $1,121.60   $1,121.50