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 $222.81   8.459%   $241.6575   $241.66   $241.65   $241.70  
  Purchase #2 $162.80   8.816%   $177.1524   $177.15   $177.15   $177.20  
  Purchase #3 $141.98   8.179%   $153.5925   $153.59   $153.60   $153.60  
  Purchase #4 $250.54   13.489%   $284.3353   $284.34   $284.35   $284.30  
  Purchase #5 $107.79   4.386%   $112.5177   $112.52   $112.50   $112.50  
  Purchase #6 $10.42   10.397%   $11.5034   $11.50   $11.50   $11.50  
  Purchase #7 $227.88   4.160%   $237.3598   $237.36   $237.35   $237.40  
  7 purchase totals = $1,124.22       $1,218.1186   $1,218.12   $1,218.10   $1,218.20