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 $138.58   9.409%   $151.619   $151.62   $151.60   $151.60  
  Purchase #2 $183.58   6.742%   $195.957   $195.96   $195.95   $196.00  
  Purchase #3 $143.54   9.686%   $157.4433   $157.44   $157.45   $157.40  
  Purchase #4 $58.26   10.719%   $64.5049   $64.50   $64.50   $64.50  
  Purchase #5 $149.84   6.273%   $159.2395   $159.24   $159.25   $159.20  
  Purchase #6 $126.79   8.102%   $137.0625   $137.06   $137.05   $137.10  
  Purchase #7 $227.55   7.164%   $243.8517   $243.85   $243.85   $243.90  
  7 purchase totals = $1,028.14       $1,109.6779   $1,109.67   $1,109.65   $1,109.70