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 $24.45   9.260%   $26.7141   $26.71   $26.70   $26.70  
  Purchase #2 $219.79   11.598%   $245.2812   $245.28   $245.30   $245.30  
  Purchase #3 $119.61   9.394%   $130.8462   $130.85   $130.85   $130.80  
  Purchase #4 $205.52   6.371%   $218.6137   $218.61   $218.60   $218.60  
  Purchase #5 $11.64   9.175%   $12.708   $12.71   $12.70   $12.70  
  Purchase #6 $88.76   10.125%   $97.747   $97.75   $97.75   $97.70  
  Purchase #7 $171.45   5.281%   $180.5043   $180.50   $180.50   $180.50  
  7 purchase totals = $841.22       $912.4145   $912.41   $912.40   $912.30