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 $232.77   12.190%   $261.1447   $261.14   $261.15   $261.10  
  Purchase #2 $148.89   7.662%   $160.298   $160.30   $160.30   $160.30  
  Purchase #3 $19.35   12.588%   $21.7858   $21.79   $21.80   $21.80  
  Purchase #4 $84.31   9.777%   $92.553   $92.55   $92.55   $92.60  
  Purchase #5 $243.50   10.819%   $269.8443   $269.84   $269.85   $269.80  
  Purchase #6 $210.42   9.559%   $230.534   $230.53   $230.55   $230.50  
  Purchase #7 $147.48   7.817%   $159.0085   $159.01   $159.00   $159.00  
  7 purchase totals = $1,086.72       $1,195.1683   $1,195.16   $1,195.20   $1,195.10