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 $126.25   5.391%   $133.0561   $133.06   $133.05   $133.10  
  Purchase #2 $168.41   4.661%   $176.2596   $176.26   $176.25   $176.30  
  Purchase #3 $164.40   6.352%   $174.8427   $174.84   $174.85   $174.80  
  Purchase #4 $231.68   13.327%   $262.556   $262.56   $262.55   $262.60  
  Purchase #5 $32.85   13.643%   $37.3317   $37.33   $37.35   $37.30  
  Purchase #6 $126.80   7.499%   $136.3087   $136.31   $136.30   $136.30  
  Purchase #7 $64.38   11.706%   $71.9163   $71.92   $71.90   $71.90  
  7 purchase totals = $914.77       $992.2711   $992.28   $992.25   $992.30