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 $76.98   13.461%   $87.3423   $87.34   $87.35   $87.30  
  Purchase #2 $157.52   11.132%   $175.0551   $175.06   $175.05   $175.10  
  Purchase #3 $107.98   9.493%   $118.2305   $118.23   $118.25   $118.20  
  Purchase #4 $106.73   8.681%   $115.9952   $116.00   $116.00   $116.00  
  Purchase #5 $225.79   10.854%   $250.2972   $250.30   $250.30   $250.30  
  Purchase #6 $147.78   4.478%   $154.3976   $154.40   $154.40   $154.40  
  Purchase #7 $141.67   8.684%   $153.9726   $153.97   $153.95   $154.00  
  7 purchase totals = $964.45       $1,055.2905   $1,055.30   $1,055.30   $1,055.30