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 $60.81   5.783%   $64.3266   $64.33   $64.35   $64.30  
  Purchase #2 $181.65   4.838%   $190.4382   $190.44   $190.45   $190.40  
  Purchase #3 $154.40   13.127%   $174.6681   $174.67   $174.65   $174.70  
  Purchase #4 $121.48   3.686%   $125.9578   $125.96   $125.95   $126.00  
  Purchase #5 $133.32   9.692%   $146.2414   $146.24   $146.25   $146.20  
  Purchase #6 $67.79   4.843%   $71.0731   $71.07   $71.05   $71.10  
  Purchase #7 $159.91   8.808%   $173.9949   $173.99   $174.00   $174.00  
  7 purchase totals = $879.36       $946.7001   $946.70   $946.70   $946.70