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 $240.56   7.391%   $258.3398   $258.34   $258.35   $258.30  
  Purchase #2 $35.72   6.383%   $38   $38.00   $38.00   $38.00  
  Purchase #3 $72.85   6.106%   $77.2982   $77.30   $77.30   $77.30  
  Purchase #4 $174.32   9.695%   $191.2203   $191.22   $191.20   $191.20  
  Purchase #5 $235.51   13.401%   $267.0707   $267.07   $267.05   $267.10  
  Purchase #6 $10.30   3.851%   $10.6967   $10.70   $10.70   $10.70  
  Purchase #7 $199.65   9.721%   $219.058   $219.06   $219.05   $219.10  
  7 purchase totals = $968.91       $1,061.6837   $1,061.69   $1,061.65   $1,061.70