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 $41.29   7.292%   $44.3009   $44.30   $44.30   $44.30  
  Purchase #2 $5.77   6.227%   $6.1293   $6.13   $6.15   $6.10  
  Purchase #3 $245.45   6.455%   $261.2938   $261.29   $261.30   $261.30  
  Purchase #4 $187.82   4.106%   $195.5319   $195.53   $195.55   $195.50  
  Purchase #5 $122.64   12.590%   $138.0804   $138.08   $138.10   $138.10  
  Purchase #6 $237.93   10.518%   $262.9555   $262.96   $262.95   $263.00  
  Purchase #7 $83.26   11.506%   $92.8399   $92.84   $92.85   $92.80  
  7 purchase totals = $924.16       $1,001.1317   $1,001.13   $1,001.20   $1,001.10