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 $64.69   12.851%   $73.0033   $73.00   $73.00   $73.00  
  Purchase #2 $215.66   7.601%   $232.0523   $232.05   $232.05   $232.10  
  Purchase #3 $78.94   12.492%   $88.8012   $88.80   $88.80   $88.80  
  Purchase #4 $159.56   3.149%   $164.5845   $164.58   $164.60   $164.60  
  Purchase #5 $65.61   3.121%   $67.6577   $67.66   $67.65   $67.70  
  Purchase #6 $97.33   13.674%   $110.6389   $110.64   $110.65   $110.60  
  Purchase #7 $124.55   13.237%   $141.0367   $141.04   $141.05   $141.00  
  7 purchase totals = $806.34       $877.7746   $877.77   $877.80   $877.80