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 $23.36   3.847%   $24.2587   $24.26   $24.25   $24.30  
  Purchase #2 $163.33   12.627%   $183.9537   $183.95   $183.95   $184.00  
  Purchase #3 $195.31   11.549%   $217.8664   $217.87   $217.85   $217.90  
  Purchase #4 $182.88   7.803%   $197.1501   $197.15   $197.15   $197.20  
  Purchase #5 $126.28   7.127%   $135.28   $135.28   $135.30   $135.30  
  Purchase #6 $189.30   9.838%   $207.9233   $207.92   $207.90   $207.90  
  Purchase #7 $236.34   3.495%   $244.6001   $244.60   $244.60   $244.60  
  7 purchase totals = $1,116.80       $1,211.0323   $1,211.03   $1,211.00   $1,211.20