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 $125.86   9.288%   $137.5499   $137.55   $137.55   $137.50  
  Purchase #2 $203.56   9.644%   $223.1913   $223.19   $223.20   $223.20  
  Purchase #3 $161.56   10.446%   $178.4366   $178.44   $178.45   $178.40  
  Purchase #4 $88.50   10.422%   $97.7235   $97.72   $97.70   $97.70  
  Purchase #5 $86.92   8.783%   $94.5542   $94.55   $94.55   $94.60  
  Purchase #6 $5.85   11.223%   $6.5065   $6.51   $6.50   $6.50  
  Purchase #7 $25.27   6.845%   $26.9997   $27.00   $27.00   $27.00  
  7 purchase totals = $697.52       $764.9617   $764.96   $764.95   $764.90