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 $34.35   10.713%   $38.0299   $38.03   $38.05   $38.00  
  Purchase #2 $103.91   11.545%   $115.9064   $115.91   $115.90   $115.90  
  Purchase #3 $226.49   4.448%   $236.5643   $236.56   $236.55   $236.60  
  Purchase #4 $46.97   8.270%   $50.8544   $50.85   $50.85   $50.90  
  Purchase #5 $83.93   10.461%   $92.7099   $92.71   $92.70   $92.70  
  Purchase #6 $182.47   7.147%   $195.5111   $195.51   $195.50   $195.50  
  Purchase #7 $88.81   8.220%   $96.1102   $96.11   $96.10   $96.10  
  7 purchase totals = $766.93       $825.6862   $825.68   $825.65   $825.70