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 $59.84   6.612%   $63.7966   $63.80   $63.80   $63.80  
  Purchase #2 $10.78   10.750%   $11.9389   $11.94   $11.95   $11.90  
  Purchase #3 $203.51   7.520%   $218.814   $218.81   $218.80   $218.80  
  Purchase #4 $220.53   8.272%   $238.7722   $238.77   $238.75   $238.80  
  Purchase #5 $231.79   6.626%   $247.1484   $247.15   $247.15   $247.10  
  Purchase #6 $92.54   4.637%   $96.8311   $96.83   $96.85   $96.80  
  Purchase #7 $53.88   8.864%   $58.6559   $58.66   $58.65   $58.70  
  7 purchase totals = $872.87       $935.9571   $935.96   $935.95   $935.90