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 $232.70   12.403%   $261.5618   $261.56   $261.55   $261.60  
  Purchase #2 $174.37   4.742%   $182.6386   $182.64   $182.65   $182.60  
  Purchase #3 $12.94   9.858%   $14.2156   $14.22   $14.20   $14.20  
  Purchase #4 $31.39   10.817%   $34.7855   $34.79   $34.80   $34.80  
  Purchase #5 $171.87   8.779%   $186.9585   $186.96   $186.95   $187.00  
  Purchase #6 $131.29   8.473%   $142.4142   $142.41   $142.40   $142.40  
  Purchase #7 $23.79   8.113%   $25.7201   $25.72   $25.70   $25.70  
  7 purchase totals = $778.35       $848.2943   $848.30   $848.25   $848.30