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 $31.27   12.737%   $35.2529   $35.25   $35.25   $35.30  
  Purchase #2 $178.39   10.740%   $197.5491   $197.55   $197.55   $197.50  
  Purchase #3 $222.73   11.869%   $249.1658   $249.17   $249.15   $249.20  
  Purchase #4 $239.43   11.296%   $266.476   $266.48   $266.50   $266.50  
  Purchase #5 $141.40   8.343%   $153.197   $153.20   $153.20   $153.20  
  Purchase #6 $209.71   12.416%   $235.7476   $235.75   $235.75   $235.70  
  Purchase #7 $63.49   5.251%   $66.8239   $66.82   $66.80   $66.80  
  7 purchase totals = $1,086.42       $1,204.2123   $1,204.22   $1,204.20   $1,204.20