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 $88.97   4.524%   $92.995   $93.00   $93.00   $93.00  
  Purchase #2 $234.78   3.653%   $243.3565   $243.36   $243.35   $243.40  
  Purchase #3 $64.48   7.397%   $69.2496   $69.25   $69.25   $69.20  
  Purchase #4 $132.62   9.359%   $145.0319   $145.03   $145.05   $145.00  
  Purchase #5 $249.29   6.850%   $266.3664   $266.37   $266.35   $266.40  
  Purchase #6 $166.46   12.448%   $187.1809   $187.18   $187.20   $187.20  
  Purchase #7 $14.87   12.672%   $16.7543   $16.75   $16.75   $16.80  
  7 purchase totals = $951.47       $1,020.9346   $1,020.94   $1,020.95   $1,021.00