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 $110.60   6.654%   $117.9593   $117.96   $117.95   $118.00  
  Purchase #2 $82.81   13.538%   $94.0208   $94.02   $94.00   $94.00  
  Purchase #3 $168.94   9.178%   $184.4453   $184.45   $184.45   $184.40  
  Purchase #4 $213.43   9.292%   $233.2619   $233.26   $233.25   $233.30  
  Purchase #5 $29.82   3.822%   $30.9597   $30.96   $30.95   $31.00  
  Purchase #6 $55.61   4.203%   $57.9473   $57.95   $57.95   $57.90  
  Purchase #7 $104.64   11.283%   $116.4465   $116.45   $116.45   $116.40  
  7 purchase totals = $765.85       $835.0408   $835.05   $835.00   $835.00