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 $54.75   12.357%   $61.5155   $61.52   $61.50   $61.50  
  Purchase #2 $87.97   7.482%   $94.5519   $94.55   $94.55   $94.60  
  Purchase #3 $189.32   4.744%   $198.3013   $198.30   $198.30   $198.30  
  Purchase #4 $68.63   5.187%   $72.1898   $72.19   $72.20   $72.20  
  Purchase #5 $11.29   4.712%   $11.822   $11.82   $11.80   $11.80  
  Purchase #6 $97.66   4.646%   $102.1973   $102.20   $102.20   $102.20  
  Purchase #7 $240.58   6.198%   $255.4911   $255.49   $255.50   $255.50  
  7 purchase totals = $750.20       $796.0689   $796.07   $796.05   $796.10