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 $62.46   6.307%   $66.3994   $66.40   $66.40   $66.40  
  Purchase #2 $148.38   11.692%   $165.7286   $165.73   $165.75   $165.70  
  Purchase #3 $35.43   8.578%   $38.4692   $38.47   $38.45   $38.50  
  Purchase #4 $220.45   5.677%   $232.9649   $232.96   $232.95   $233.00  
  Purchase #5 $22.73   11.619%   $25.371   $25.37   $25.35   $25.40  
  Purchase #6 $192.31   9.577%   $210.7275   $210.73   $210.75   $210.70  
  Purchase #7 $103.28   8.712%   $112.2778   $112.28   $112.30   $112.30  
  7 purchase totals = $785.04       $851.9384   $851.94   $851.95   $852.00