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 $52.59   10.794%   $58.2666   $58.27   $58.25   $58.30  
  Purchase #2 $187.34   8.161%   $202.6288   $202.63   $202.65   $202.60  
  Purchase #3 $63.40   13.631%   $72.0421   $72.04   $72.05   $72.00  
  Purchase #4 $235.37   11.466%   $262.3575   $262.36   $262.35   $262.40  
  Purchase #5 $35.36   12.226%   $39.6831   $39.68   $39.70   $39.70  
  Purchase #6 $24.43   9.236%   $26.6864   $26.69   $26.70   $26.70  
  Purchase #7 $159.51   8.850%   $173.6266   $173.63   $173.65   $173.60  
  7 purchase totals = $758.00       $835.2911   $835.30   $835.35   $835.30