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 $125.46   12.632%   $141.3081   $141.31   $141.30   $141.30  
  Purchase #2 $43.32   6.868%   $46.2952   $46.30   $46.30   $46.30  
  Purchase #3 $22.29   3.530%   $23.0768   $23.08   $23.10   $23.10  
  Purchase #4 $42.37   3.273%   $43.7568   $43.76   $43.75   $43.80  
  Purchase #5 $11.30   6.607%   $12.0466   $12.05   $12.05   $12.00  
  Purchase #6 $150.79   8.289%   $163.289   $163.29   $163.30   $163.30  
  Purchase #7 $164.48   6.704%   $175.5067   $175.51   $175.50   $175.50  
  7 purchase totals = $560.01       $605.2792   $605.30   $605.30   $605.30