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 $83.86   11.567%   $93.5601   $93.56   $93.55   $93.60  
  Purchase #2 $116.89   7.758%   $125.9583   $125.96   $125.95   $126.00  
  Purchase #3 $81.38   3.760%   $84.4399   $84.44   $84.45   $84.40  
  Purchase #4 $174.66   6.184%   $185.461   $185.46   $185.45   $185.50  
  Purchase #5 $113.75   3.570%   $117.8109   $117.81   $117.80   $117.80  
  Purchase #6 $38.70   5.694%   $40.9036   $40.90   $40.90   $40.90  
  Purchase #7 $157.88   10.636%   $174.6721   $174.67   $174.65   $174.70  
  7 purchase totals = $767.12       $822.8059   $822.80   $822.75   $822.90