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 $74.35   12.253%   $83.4601   $83.46   $83.45   $83.50  
  Purchase #2 $123.95   12.674%   $139.6594   $139.66   $139.65   $139.70  
  Purchase #3 $112.35   12.858%   $126.796   $126.80   $126.80   $126.80  
  Purchase #4 $180.76   7.854%   $194.9569   $194.96   $194.95   $195.00  
  Purchase #5 $183.64   8.797%   $199.7948   $199.79   $199.80   $199.80  
  Purchase #6 $72.79   6.572%   $77.5738   $77.57   $77.55   $77.60  
  Purchase #7 $123.93   13.136%   $140.2094   $140.21   $140.20   $140.20  
  7 purchase totals = $871.77       $962.4504   $962.45   $962.40   $962.60