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 $42.29   10.229%   $46.6158   $46.62   $46.60   $46.60  
  Purchase #2 $58.62   12.556%   $65.9803   $65.98   $66.00   $66.00  
  Purchase #3 $149.34   4.868%   $156.6099   $156.61   $156.60   $156.60  
  Purchase #4 $225.68   8.138%   $244.0458   $244.05   $244.05   $244.00  
  Purchase #5 $234.73   7.309%   $251.8864   $251.89   $251.90   $251.90  
  Purchase #6 $166.80   4.789%   $174.7881   $174.79   $174.80   $174.80  
  Purchase #7 $89.25   9.645%   $97.8582   $97.86   $97.85   $97.90  
  7 purchase totals = $966.71       $1,037.7845   $1,037.80   $1,037.80   $1,037.80