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 $248.84   8.187%   $269.2125   $269.21   $269.20   $269.20  
  Purchase #2 $163.56   7.527%   $175.8712   $175.87   $175.85   $175.90  
  Purchase #3 $111.45   4.544%   $116.5143   $116.51   $116.50   $116.50  
  Purchase #4 $240.68   9.668%   $263.9489   $263.95   $263.95   $263.90  
  Purchase #5 $67.29   7.302%   $72.2035   $72.20   $72.20   $72.20  
  Purchase #6 $212.73   4.396%   $222.0816   $222.08   $222.10   $222.10  
  Purchase #7 $126.94   11.786%   $141.9011   $141.90   $141.90   $141.90  
  7 purchase totals = $1,171.49       $1,261.7331   $1,261.72   $1,261.70   $1,261.70