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 $223.64   12.674%   $251.9841   $251.98   $252.00   $252.00  
  Purchase #2 $138.62   12.626%   $156.1222   $156.12   $156.10   $156.10  
  Purchase #3 $83.63   11.140%   $92.9464   $92.95   $92.95   $92.90  
  Purchase #4 $23.34   3.617%   $24.1842   $24.18   $24.20   $24.20  
  Purchase #5 $34.62   4.345%   $36.1242   $36.12   $36.10   $36.10  
  Purchase #6 $153.95   13.660%   $174.9796   $174.98   $175.00   $175.00  
  Purchase #7 $16.54   10.455%   $18.2693   $18.27   $18.25   $18.30  
  7 purchase totals = $674.34       $754.6100   $754.60   $754.60   $754.60