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 $170.56   8.604%   $185.235   $185.24   $185.25   $185.20  
  Purchase #2 $223.51   5.276%   $235.3024   $235.30   $235.30   $235.30  
  Purchase #3 $220.70   6.370%   $234.7586   $234.76   $234.75   $234.80  
  Purchase #4 $227.80   8.692%   $247.6004   $247.60   $247.60   $247.60  
  Purchase #5 $121.56   9.854%   $133.5385   $133.54   $133.55   $133.50  
  Purchase #6 $249.86   10.159%   $275.2433   $275.24   $275.25   $275.20  
  Purchase #7 $74.39   4.378%   $77.6468   $77.65   $77.65   $77.60  
  7 purchase totals = $1,288.38       $1,389.3250   $1,389.33   $1,389.35   $1,389.20