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 $245.31   6.780%   $261.942   $261.94   $261.95   $261.90  
  Purchase #2 $111.50   7.161%   $119.4845   $119.48   $119.50   $119.50  
  Purchase #3 $170.79   9.343%   $186.7469   $186.75   $186.75   $186.70  
  Purchase #4 $168.60   11.385%   $187.7951   $187.80   $187.80   $187.80  
  Purchase #5 $65.38   5.539%   $69.0014   $69.00   $69.00   $69.00  
  Purchase #6 $220.52   4.519%   $230.4853   $230.49   $230.50   $230.50  
  Purchase #7 $94.79   11.109%   $105.3202   $105.32   $105.30   $105.30  
  7 purchase totals = $1,076.89       $1,160.7754   $1,160.78   $1,160.80   $1,160.70