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 $240.43   11.466%   $267.9977   $268.00   $268.00   $268.00  
  Purchase #2 $215.84   9.707%   $236.7916   $236.79   $236.80   $236.80  
  Purchase #3 $149.93   9.315%   $163.896   $163.90   $163.90   $163.90  
  Purchase #4 $249.80   9.196%   $272.7716   $272.77   $272.75   $272.80  
  Purchase #5 $58.73   13.318%   $66.5517   $66.55   $66.55   $66.60  
  Purchase #6 $127.55   10.232%   $140.6009   $140.60   $140.60   $140.60  
  Purchase #7 $31.41   3.526%   $32.5175   $32.52   $32.50   $32.50  
  7 purchase totals = $1,073.69       $1,181.1270   $1,181.13   $1,181.10   $1,181.20