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 $210.65   10.676%   $233.139   $233.14   $233.15   $233.10  
  Purchase #2 $77.26   7.344%   $82.934   $82.93   $82.95   $82.90  
  Purchase #3 $35.77   3.700%   $37.0935   $37.09   $37.10   $37.10  
  Purchase #4 $243.89   5.466%   $257.221   $257.22   $257.20   $257.20  
  Purchase #5 $237.86   3.211%   $245.4977   $245.50   $245.50   $245.50  
  Purchase #6 $31.88   8.710%   $34.6567   $34.66   $34.65   $34.70  
  Purchase #7 $135.62   8.634%   $147.3294   $147.33   $147.35   $147.30  
  7 purchase totals = $972.93       $1,037.8713   $1,037.87   $1,037.90   $1,037.80