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 $93.95   13.640%   $106.7648   $106.76   $106.75   $106.80  
  Purchase #2 $141.94   12.272%   $159.3589   $159.36   $159.35   $159.40  
  Purchase #3 $22.48   11.705%   $25.1113   $25.11   $25.10   $25.10  
  Purchase #4 $152.91   11.481%   $170.4656   $170.47   $170.45   $170.50  
  Purchase #5 $14.75   7.815%   $15.9027   $15.90   $15.90   $15.90  
  Purchase #6 $11.31   10.845%   $12.5366   $12.54   $12.55   $12.50  
  Purchase #7 $85.58   7.447%   $91.9531   $91.95   $91.95   $92.00  
  7 purchase totals = $522.92       $582.0930   $582.09   $582.05   $582.20