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 $140.91   7.318%   $151.2218   $151.22   $151.20   $151.20  
  Purchase #2 $209.53   11.447%   $233.5149   $233.51   $233.50   $233.50  
  Purchase #3 $58.75   4.764%   $61.5489   $61.55   $61.55   $61.50  
  Purchase #4 $171.52   12.264%   $192.5552   $192.56   $192.55   $192.60  
  Purchase #5 $23.72   9.569%   $25.9898   $25.99   $26.00   $26.00  
  Purchase #6 $65.90   8.647%   $71.5984   $71.60   $71.60   $71.60  
  Purchase #7 $15.40   6.184%   $16.3523   $16.35   $16.35   $16.40  
  7 purchase totals = $685.73       $752.7813   $752.78   $752.75   $752.80