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 $187.95   11.464%   $209.4966   $209.50   $209.50   $209.50  
  Purchase #2 $216.93   8.611%   $235.6098   $235.61   $235.60   $235.60  
  Purchase #3 $120.49   5.206%   $126.7627   $126.76   $126.75   $126.80  
  Purchase #4 $111.62   4.761%   $116.9342   $116.93   $116.95   $116.90  
  Purchase #5 $152.46   9.192%   $166.4741   $166.47   $166.45   $166.50  
  Purchase #6 $11.59   4.310%   $12.0895   $12.09   $12.10   $12.10  
  Purchase #7 $86.95   7.158%   $93.1739   $93.17   $93.15   $93.20  
  7 purchase totals = $887.99       $960.5408   $960.53   $960.50   $960.60