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 $53.67   7.217%   $57.5434   $57.54   $57.55   $57.50  
  Purchase #2 $163.32   11.636%   $182.3239   $182.32   $182.30   $182.30  
  Purchase #3 $220.32   5.329%   $232.0609   $232.06   $232.05   $232.10  
  Purchase #4 $193.93   10.518%   $214.3276   $214.33   $214.35   $214.30  
  Purchase #5 $240.62   13.299%   $272.6201   $272.62   $272.60   $272.60  
  Purchase #6 $173.71   10.696%   $192.29   $192.29   $192.30   $192.30  
  Purchase #7 $129.88   11.245%   $144.485   $144.49   $144.50   $144.50  
  7 purchase totals = $1,175.45       $1,295.6509   $1,295.65   $1,295.65   $1,295.60