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 $86.32   7.554%   $92.8406   $92.84   $92.85   $92.80  
  Purchase #2 $53.32   13.483%   $60.5091   $60.51   $60.50   $60.50  
  Purchase #3 $239.31   13.789%   $272.3085   $272.31   $272.30   $272.30  
  Purchase #4 $118.95   11.603%   $132.7518   $132.75   $132.75   $132.80  
  Purchase #5 $104.80   9.450%   $114.7036   $114.70   $114.70   $114.70  
  Purchase #6 $179.72   12.677%   $202.5031   $202.50   $202.50   $202.50  
  Purchase #7 $48.29   11.293%   $53.7434   $53.74   $53.75   $53.70  
  7 purchase totals = $830.71       $929.3601   $929.35   $929.35   $929.30