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 $63.93   3.277%   $66.025   $66.03   $66.05   $66.00  
  Purchase #2 $228.42   4.307%   $238.258   $238.26   $238.25   $238.30  
  Purchase #3 $41.79   5.410%   $44.0508   $44.05   $44.05   $44.10  
  Purchase #4 $165.29   5.104%   $173.7264   $173.73   $173.75   $173.70  
  Purchase #5 $174.25   8.840%   $189.6537   $189.65   $189.65   $189.70  
  Purchase #6 $111.35   8.697%   $121.0341   $121.03   $121.05   $121.00  
  Purchase #7 $114.73   12.795%   $129.4097   $129.41   $129.40   $129.40  
  7 purchase totals = $899.76       $962.1577   $962.16   $962.20   $962.20