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 $241.34   4.860%   $253.0691   $253.07   $253.05   $253.10  
  Purchase #2 $58.31   13.295%   $66.0623   $66.06   $66.05   $66.10  
  Purchase #3 $194.54   4.643%   $203.5725   $203.57   $203.55   $203.60  
  Purchase #4 $149.77   7.197%   $160.5489   $160.55   $160.55   $160.50  
  Purchase #5 $179.48   11.191%   $199.5656   $199.57   $199.55   $199.60  
  Purchase #6 $42.67   3.446%   $44.1404   $44.14   $44.15   $44.10  
  Purchase #7 $200.47   10.398%   $221.3149   $221.31   $221.30   $221.30  
  7 purchase totals = $1,066.58       $1,148.2737   $1,148.27   $1,148.20   $1,148.30