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 $52.36   8.168%   $56.6368   $56.64   $56.65   $56.60  
  Purchase #2 $28.69   12.355%   $32.2346   $32.23   $32.25   $32.20  
  Purchase #3 $45.36   13.764%   $51.6034   $51.60   $51.60   $51.60  
  Purchase #4 $234.64   6.800%   $250.5955   $250.60   $250.60   $250.60  
  Purchase #5 $63.58   9.374%   $69.54   $69.54   $69.55   $69.50  
  Purchase #6 $232.52   9.403%   $254.3839   $254.38   $254.40   $254.40  
  Purchase #7 $219.76   8.732%   $238.9494   $238.95   $238.95   $238.90  
  7 purchase totals = $876.91       $953.9436   $953.94   $954.00   $953.80