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 $52.58   13.731%   $59.7998   $59.80   $59.80   $59.80  
  Purchase #2 $249.63   7.531%   $268.4296   $268.43   $268.45   $268.40  
  Purchase #3 $115.69   6.725%   $123.4702   $123.47   $123.45   $123.50  
  Purchase #4 $231.31   5.116%   $243.1438   $243.14   $243.15   $243.10  
  Purchase #5 $133.88   7.726%   $144.2236   $144.22   $144.20   $144.20  
  Purchase #6 $169.87   7.141%   $182.0004   $182.00   $182.00   $182.00  
  Purchase #7 $197.93   7.206%   $212.1928   $212.19   $212.20   $212.20  
  7 purchase totals = $1,150.89       $1,233.2602   $1,233.25   $1,233.25   $1,233.20