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 $133.54   13.494%   $151.5599   $151.56   $151.55   $151.60  
  Purchase #2 $66.43   6.812%   $70.9552   $70.96   $70.95   $71.00  
  Purchase #3 $216.40   9.511%   $236.9818   $236.98   $237.00   $237.00  
  Purchase #4 $245.90   7.137%   $263.4499   $263.45   $263.45   $263.40  
  Purchase #5 $221.39   12.825%   $249.7833   $249.78   $249.80   $249.80  
  Purchase #6 $42.32   6.517%   $45.078   $45.08   $45.10   $45.10  
  Purchase #7 $105.46   9.797%   $115.7919   $115.79   $115.80   $115.80  
  7 purchase totals = $1,031.44       $1,133.6000   $1,133.60   $1,133.65   $1,133.70