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 $135.90   6.863%   $145.2268   $145.23   $145.25   $145.20  
  Purchase #2 $169.92   13.833%   $193.425   $193.43   $193.45   $193.40  
  Purchase #3 $42.49   6.194%   $45.1218   $45.12   $45.10   $45.10  
  Purchase #4 $244.32   3.587%   $253.0838   $253.08   $253.10   $253.10  
  Purchase #5 $92.63   3.559%   $95.9267   $95.93   $95.95   $95.90  
  Purchase #6 $245.81   4.163%   $256.0431   $256.04   $256.05   $256.00  
  Purchase #7 $56.51   6.238%   $60.0351   $60.04   $60.05   $60.00  
  7 purchase totals = $987.58       $1,048.8623   $1,048.87   $1,048.95   $1,048.70