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 $208.34   12.696%   $234.7908   $234.79   $234.80   $234.80  
  Purchase #2 $184.75   5.822%   $195.5061   $195.51   $195.50   $195.50  
  Purchase #3 $229.77   9.522%   $251.6487   $251.65   $251.65   $251.60  
  Purchase #4 $109.67   5.340%   $115.5264   $115.53   $115.55   $115.50  
  Purchase #5 $123.64   4.217%   $128.8539   $128.85   $128.85   $128.90  
  Purchase #6 $26.60   6.239%   $28.2596   $28.26   $28.25   $28.30  
  Purchase #7 $215.82   12.117%   $241.9709   $241.97   $241.95   $242.00  
  7 purchase totals = $1,098.59       $1,196.5564   $1,196.56   $1,196.55   $1,196.60