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 $62.90   6.831%   $67.1967   $67.20   $67.20   $67.20  
  Purchase #2 $54.66   3.634%   $56.6463   $56.65   $56.65   $56.60  
  Purchase #3 $179.71   6.352%   $191.1252   $191.13   $191.15   $191.10  
  Purchase #4 $58.53   3.669%   $60.6775   $60.68   $60.70   $60.70  
  Purchase #5 $247.47   4.645%   $258.965   $258.97   $258.95   $259.00  
  Purchase #6 $128.97   13.552%   $146.448   $146.45   $146.45   $146.40  
  Purchase #7 $64.74   13.850%   $73.7065   $73.71   $73.70   $73.70  
  7 purchase totals = $796.98       $854.7652   $854.79   $854.80   $854.70