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 $141.89   9.148%   $154.8701   $154.87   $154.85   $154.90  
  Purchase #2 $201.95   3.637%   $209.2949   $209.29   $209.30   $209.30  
  Purchase #3 $169.99   11.527%   $189.5847   $189.58   $189.60   $189.60  
  Purchase #4 $232.61   11.725%   $259.8835   $259.88   $259.90   $259.90  
  Purchase #5 $118.98   4.347%   $124.1521   $124.15   $124.15   $124.20  
  Purchase #6 $62.94   13.469%   $71.4174   $71.42   $71.40   $71.40  
  Purchase #7 $80.57   13.863%   $91.7394   $91.74   $91.75   $91.70  
  7 purchase totals = $1,008.93       $1,100.9421   $1,100.93   $1,100.95   $1,101.00