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 $235.77   10.803%   $261.2402   $261.24   $261.25   $261.20  
  Purchase #2 $173.59   6.484%   $184.8456   $184.85   $184.85   $184.80  
  Purchase #3 $11.64   5.792%   $12.3142   $12.31   $12.30   $12.30  
  Purchase #4 $240.62   9.657%   $263.8567   $263.86   $263.85   $263.90  
  Purchase #5 $206.95   12.597%   $233.0195   $233.02   $233.00   $233.00  
  Purchase #6 $144.79   11.804%   $161.881   $161.88   $161.90   $161.90  
  Purchase #7 $122.56   9.311%   $133.9716   $133.97   $133.95   $134.00  
  7 purchase totals = $1,135.92       $1,251.1288   $1,251.13   $1,251.10   $1,251.10