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 $29.89   8.767%   $32.5105   $32.51   $32.50   $32.50  
  Purchase #2 $141.36   12.239%   $158.6611   $158.66   $158.65   $158.70  
  Purchase #3 $128.41   13.527%   $145.78   $145.78   $145.80   $145.80  
  Purchase #4 $143.26   11.117%   $159.1862   $159.19   $159.20   $159.20  
  Purchase #5 $106.36   6.547%   $113.3234   $113.32   $113.30   $113.30  
  Purchase #6 $163.72   11.541%   $182.6149   $182.61   $182.60   $182.60  
  Purchase #7 $184.56   10.642%   $204.2009   $204.20   $204.20   $204.20  
  7 purchase totals = $897.56       $996.2770   $996.27   $996.25   $996.30