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 $68.98   6.610%   $73.5396   $73.54   $73.55   $73.50  
  Purchase #2 $188.58   6.855%   $201.5072   $201.51   $201.50   $201.50  
  Purchase #3 $63.50   12.294%   $71.3067   $71.31   $71.30   $71.30  
  Purchase #4 $67.68   10.638%   $74.8798   $74.88   $74.90   $74.90  
  Purchase #5 $175.56   10.468%   $193.9376   $193.94   $193.95   $193.90  
  Purchase #6 $250.48   8.386%   $271.4853   $271.49   $271.50   $271.50  
  Purchase #7 $129.66   6.474%   $138.0542   $138.05   $138.05   $138.10  
  7 purchase totals = $944.44       $1,024.7104   $1,024.72   $1,024.75   $1,024.70