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 $185.46   8.111%   $200.5027   $200.50   $200.50   $200.50  
  Purchase #2 $68.63   10.451%   $75.8025   $75.80   $75.80   $75.80  
  Purchase #3 $216.65   8.320%   $234.6753   $234.68   $234.70   $234.70  
  Purchase #4 $41.52   8.680%   $45.1239   $45.12   $45.10   $45.10  
  Purchase #5 $73.72   6.182%   $78.2774   $78.28   $78.30   $78.30  
  Purchase #6 $96.98   13.446%   $110.0199   $110.02   $110.00   $110.00  
  Purchase #7 $211.59   8.277%   $229.1033   $229.10   $229.10   $229.10  
  7 purchase totals = $894.55       $973.5050   $973.50   $973.50   $973.50