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 $201.33   13.367%   $228.2418   $228.24   $228.25   $228.20  
  Purchase #2 $22.76   9.312%   $24.8794   $24.88   $24.90   $24.90  
  Purchase #3 $30.36   10.784%   $33.634   $33.63   $33.65   $33.60  
  Purchase #4 $69.42   5.695%   $73.3735   $73.37   $73.35   $73.40  
  Purchase #5 $166.94   9.378%   $182.5956   $182.60   $182.60   $182.60  
  Purchase #6 $8.42   10.217%   $9.2803   $9.28   $9.30   $9.30  
  Purchase #7 $197.69   3.694%   $204.9927   $204.99   $205.00   $205.00  
  7 purchase totals = $696.92       $756.9973   $756.99   $757.05   $757.00