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   13.359%   $235.73   $235.73   $235.75   $235.70  
  Purchase #2 $26.74   12.867%   $30.1806   $30.18   $30.20   $30.20  
  Purchase #3 $152.31   11.436%   $169.7282   $169.73   $169.75   $169.70  
  Purchase #4 $188.45   9.284%   $205.9457   $205.95   $205.95   $205.90  
  Purchase #5 $238.92   3.661%   $247.6669   $247.67   $247.65   $247.70  
  Purchase #6 $100.78   3.555%   $104.3627   $104.36   $104.35   $104.40  
  Purchase #7 $206.34   11.109%   $229.2623   $229.26   $229.25   $229.30  
  7 purchase totals = $1,121.49       $1,222.8764   $1,222.88   $1,222.90   $1,222.90