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 $246.47   3.719%   $255.6362   $255.64   $255.65   $255.60  
  Purchase #2 $204.45   11.289%   $227.5304   $227.53   $227.55   $227.50  
  Purchase #3 $68.51   9.296%   $74.8787   $74.88   $74.90   $74.90  
  Purchase #4 $169.45   7.660%   $182.4299   $182.43   $182.45   $182.40  
  Purchase #5 $86.39   7.301%   $92.6973   $92.70   $92.70   $92.70  
  Purchase #6 $225.40   10.320%   $248.6613   $248.66   $248.65   $248.70  
  Purchase #7 $75.83   9.401%   $82.9588   $82.96   $82.95   $83.00  
  7 purchase totals = $1,076.50       $1,164.7926   $1,164.80   $1,164.85   $1,164.80