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 $45.42   11.147%   $50.483   $50.48   $50.50   $50.50  
  Purchase #2 $184.44   13.586%   $209.498   $209.50   $209.50   $209.50  
  Purchase #3 $24.81   6.281%   $26.3683   $26.37   $26.35   $26.40  
  Purchase #4 $167.38   3.680%   $173.5396   $173.54   $173.55   $173.50  
  Purchase #5 $153.96   9.568%   $168.6909   $168.69   $168.70   $168.70  
  Purchase #6 $236.46   3.637%   $245.0601   $245.06   $245.05   $245.10  
  Purchase #7 $66.72   3.511%   $69.0625   $69.06   $69.05   $69.10  
  7 purchase totals = $879.19       $942.7024   $942.70   $942.70   $942.80