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 $50.43   12.741%   $56.8553   $56.86   $56.85   $56.90  
  Purchase #2 $140.87   13.642%   $160.0875   $160.09   $160.10   $160.10  
  Purchase #3 $243.40   5.176%   $255.9984   $256.00   $256.00   $256.00  
  Purchase #4 $85.64   11.419%   $95.4192   $95.42   $95.40   $95.40  
  Purchase #5 $205.78   7.300%   $220.8019   $220.80   $220.80   $220.80  
  Purchase #6 $118.93   5.872%   $125.9136   $125.91   $125.90   $125.90  
  Purchase #7 $41.70   10.329%   $46.0072   $46.01   $46.00   $46.00  
  7 purchase totals = $886.75       $961.0831   $961.09   $961.05   $961.10