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 $89.84   4.115%   $93.5369   $93.54   $93.55   $93.50  
  Purchase #2 $233.91   13.301%   $265.0224   $265.02   $265.00   $265.00  
  Purchase #3 $113.59   10.497%   $125.5135   $125.51   $125.50   $125.50  
  Purchase #4 $88.27   11.249%   $98.1995   $98.20   $98.20   $98.20  
  Purchase #5 $170.31   9.232%   $186.033   $186.03   $186.05   $186.00  
  Purchase #6 $202.28   5.206%   $212.8107   $212.81   $212.80   $212.80  
  Purchase #7 $154.97   13.667%   $176.1497   $176.15   $176.15   $176.10  
  7 purchase totals = $1,053.17       $1,157.2657   $1,157.26   $1,157.25   $1,157.10