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 $164.79   9.861%   $181.0399   $181.04   $181.05   $181.00  
  Purchase #2 $117.51   11.391%   $130.8956   $130.90   $130.90   $130.90  
  Purchase #3 $39.74   4.166%   $41.3956   $41.40   $41.40   $41.40  
  Purchase #4 $221.81   6.567%   $236.3763   $236.38   $236.40   $236.40  
  Purchase #5 $163.91   8.867%   $178.4439   $178.44   $178.45   $178.40  
  Purchase #6 $30.53   11.361%   $33.9985   $34.00   $34.00   $34.00  
  Purchase #7 $243.84   5.872%   $258.1583   $258.16   $258.15   $258.20  
  7 purchase totals = $982.13       $1,060.3081   $1,060.32   $1,060.35   $1,060.30