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 $60.88   11.697%   $68.0011   $68.00   $68.00   $68.00  
  Purchase #2 $149.66   11.426%   $166.7602   $166.76   $166.75   $166.80  
  Purchase #3 $145.77   11.154%   $162.0292   $162.03   $162.05   $162.00  
  Purchase #4 $118.59   6.648%   $126.4739   $126.47   $126.45   $126.50  
  Purchase #5 $68.83   13.202%   $77.9169   $77.92   $77.90   $77.90  
  Purchase #6 $190.87   10.689%   $211.2721   $211.27   $211.25   $211.30  
  Purchase #7 $20.97   5.479%   $22.1189   $22.12   $22.10   $22.10  
  7 purchase totals = $755.57       $834.5723   $834.57   $834.50   $834.60