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 $244.46   11.262%   $271.9911   $271.99   $272.00   $272.00  
  Purchase #2 $101.95   4.123%   $106.1534   $106.15   $106.15   $106.20  
  Purchase #3 $124.51   9.704%   $136.5925   $136.59   $136.60   $136.60  
  Purchase #4 $210.62   4.381%   $219.8473   $219.85   $219.85   $219.80  
  Purchase #5 $67.77   11.268%   $75.4063   $75.41   $75.40   $75.40  
  Purchase #6 $150.73   8.392%   $163.3793   $163.38   $163.40   $163.40  
  Purchase #7 $20.70   6.488%   $22.043   $22.04   $22.05   $22.00  
  7 purchase totals = $920.74       $995.4129   $995.41   $995.45   $995.40