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 $56.62   13.556%   $64.2954   $64.30   $64.30   $64.30  
  Purchase #2 $221.68   3.249%   $228.8824   $228.88   $228.90   $228.90  
  Purchase #3 $43.58   9.329%   $47.6456   $47.65   $47.65   $47.60  
  Purchase #4 $62.59   9.788%   $68.7163   $68.72   $68.70   $68.70  
  Purchase #5 $116.30   3.581%   $120.4647   $120.46   $120.45   $120.50  
  Purchase #6 $147.95   9.440%   $161.9165   $161.92   $161.90   $161.90  
  Purchase #7 $53.62   7.385%   $57.5798   $57.58   $57.60   $57.60  
  7 purchase totals = $702.34       $749.5007   $749.51   $749.50   $749.50