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 $155.59   4.481%   $162.562   $162.56   $162.55   $162.60  
  Purchase #2 $75.46   11.836%   $84.3914   $84.39   $84.40   $84.40  
  Purchase #3 $153.28   9.385%   $167.6653   $167.67   $167.65   $167.70  
  Purchase #4 $236.31   6.863%   $252.528   $252.53   $252.55   $252.50  
  Purchase #5 $112.83   5.787%   $119.3595   $119.36   $119.35   $119.40  
  Purchase #6 $176.33   13.141%   $199.5015   $199.50   $199.50   $199.50  
  Purchase #7 $225.29   8.352%   $244.1062   $244.11   $244.10   $244.10  
  7 purchase totals = $1,135.09       $1,230.1139   $1,230.12   $1,230.10   $1,230.20