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 $227.84   11.601%   $254.2717   $254.27   $254.25   $254.30  
  Purchase #2 $126.49   7.208%   $135.6074   $135.61   $135.60   $135.60  
  Purchase #3 $80.70   13.401%   $91.5146   $91.51   $91.50   $91.50  
  Purchase #4 $113.34   3.825%   $117.6753   $117.68   $117.70   $117.70  
  Purchase #5 $176.99   10.802%   $196.1085   $196.11   $196.10   $196.10  
  Purchase #6 $129.81   7.684%   $139.7846   $139.78   $139.80   $139.80  
  Purchase #7 $59.70   11.508%   $66.5703   $66.57   $66.55   $66.60  
  7 purchase totals = $914.87       $1,001.5324   $1,001.53   $1,001.50   $1,001.60