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 $83.46   11.480%   $93.0412   $93.04   $93.05   $93.00  
  Purchase #2 $189.33   8.650%   $205.707   $205.71   $205.70   $205.70  
  Purchase #3 $106.71   8.433%   $115.7089   $115.71   $115.70   $115.70  
  Purchase #4 $104.95   9.429%   $114.8457   $114.85   $114.85   $114.80  
  Purchase #5 $176.57   3.112%   $182.0649   $182.06   $182.05   $182.10  
  Purchase #6 $49.99   3.740%   $51.8596   $51.86   $51.85   $51.90  
  Purchase #7 $245.57   10.352%   $270.9914   $270.99   $271.00   $271.00  
  7 purchase totals = $956.58       $1,034.2187   $1,034.22   $1,034.20   $1,034.20