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 $68.83   13.195%   $77.9121   $77.91   $77.90   $77.90  
  Purchase #2 $189.51   8.588%   $205.7851   $205.79   $205.80   $205.80  
  Purchase #3 $180.74   11.264%   $201.0986   $201.10   $201.10   $201.10  
  Purchase #4 $24.66   7.840%   $26.5933   $26.59   $26.60   $26.60  
  Purchase #5 $210.99   4.313%   $220.09   $220.09   $220.10   $220.10  
  Purchase #6 $98.78   13.362%   $111.979   $111.98   $112.00   $112.00  
  Purchase #7 $246.78   4.491%   $257.8629   $257.86   $257.85   $257.90  
  7 purchase totals = $1,020.29       $1,101.3210   $1,101.32   $1,101.35   $1,101.40