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 $116.91   12.140%   $131.1029   $131.10   $131.10   $131.10  
  Purchase #2 $67.31   12.385%   $75.6463   $75.65   $75.65   $75.60  
  Purchase #3 $62.43   5.240%   $65.7013   $65.70   $65.70   $65.70  
  Purchase #4 $59.77   11.493%   $66.6394   $66.64   $66.65   $66.60  
  Purchase #5 $85.86   10.601%   $94.962   $94.96   $94.95   $95.00  
  Purchase #6 $193.54   11.116%   $215.0539   $215.05   $215.05   $215.10  
  Purchase #7 $90.97   5.258%   $95.7532   $95.75   $95.75   $95.80  
  7 purchase totals = $676.79       $744.8590   $744.85   $744.85   $744.90