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 $207.95   12.427%   $233.7919   $233.79   $233.80   $233.80  
  Purchase #2 $134.90   13.790%   $153.5027   $153.50   $153.50   $153.50  
  Purchase #3 $150.77   3.553%   $156.1269   $156.13   $156.15   $156.10  
  Purchase #4 $232.86   10.295%   $256.8329   $256.83   $256.85   $256.80  
  Purchase #5 $183.92   10.767%   $203.7227   $203.72   $203.70   $203.70  
  Purchase #6 $86.40   12.808%   $97.4661   $97.47   $97.45   $97.50  
  Purchase #7 $51.36   5.409%   $54.1381   $54.14   $54.15   $54.10  
  7 purchase totals = $1,048.16       $1,155.5813   $1,155.58   $1,155.60   $1,155.50