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 $117.38   8.354%   $127.1859   $127.19   $127.20   $127.20  
  Purchase #2 $184.47   4.275%   $192.3561   $192.36   $192.35   $192.40  
  Purchase #3 $82.88   3.548%   $85.8206   $85.82   $85.80   $85.80  
  Purchase #4 $210.81   10.410%   $232.7553   $232.76   $232.75   $232.80  
  Purchase #5 $195.83   12.150%   $219.6233   $219.62   $219.60   $219.60  
  Purchase #6 $135.58   13.607%   $154.0284   $154.03   $154.05   $154.00  
  Purchase #7 $30.93   5.314%   $32.5736   $32.57   $32.55   $32.60  
  7 purchase totals = $957.88       $1,044.3432   $1,044.35   $1,044.30   $1,044.40