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 $233.37   10.690%   $258.3173   $258.32   $258.30   $258.30  
  Purchase #2 $218.84   10.409%   $241.6191   $241.62   $241.60   $241.60  
  Purchase #3 $62.93   13.612%   $71.496   $71.50   $71.50   $71.50  
  Purchase #4 $52.42   9.774%   $57.5435   $57.54   $57.55   $57.50  
  Purchase #5 $155.61   13.717%   $176.955   $176.96   $176.95   $177.00  
  Purchase #6 $171.35   10.612%   $189.5337   $189.53   $189.55   $189.50  
  Purchase #7 $231.60   8.299%   $250.8205   $250.82   $250.80   $250.80  
  7 purchase totals = $1,126.12       $1,246.2851   $1,246.29   $1,246.25   $1,246.20