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 $29.76   11.516%   $33.1872   $33.19   $33.20   $33.20  
  Purchase #2 $225.86   8.343%   $244.7035   $244.70   $244.70   $244.70  
  Purchase #3 $236.65   4.809%   $248.0305   $248.03   $248.05   $248.00  
  Purchase #4 $54.56   11.549%   $60.8611   $60.86   $60.85   $60.90  
  Purchase #5 $113.27   8.412%   $122.7983   $122.80   $122.80   $122.80  
  Purchase #6 $126.86   11.180%   $141.0429   $141.04   $141.05   $141.00  
  Purchase #7 $211.61   11.532%   $236.0129   $236.01   $236.00   $236.00  
  7 purchase totals = $998.57       $1,086.6364   $1,086.63   $1,086.65   $1,086.60