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 $68.79   6.267%   $73.1011   $73.10   $73.10   $73.10  
  Purchase #2 $178.91   8.745%   $194.5557   $194.56   $194.55   $194.60  
  Purchase #3 $139.94   4.459%   $146.1799   $146.18   $146.20   $146.20  
  Purchase #4 $135.94   7.745%   $146.4686   $146.47   $146.45   $146.50  
  Purchase #5 $153.61   3.769%   $159.3996   $159.40   $159.40   $159.40  
  Purchase #6 $67.94   5.652%   $71.78   $71.78   $71.80   $71.80  
  Purchase #7 $98.80   6.360%   $105.0837   $105.08   $105.10   $105.10  
  7 purchase totals = $843.93       $896.5686   $896.57   $896.60   $896.70