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 $87.85   10.684%   $97.2359   $97.24   $97.25   $97.20  
  Purchase #2 $160.51   5.137%   $168.7554   $168.76   $168.75   $168.80  
  Purchase #3 $46.65   7.223%   $50.0195   $50.02   $50.00   $50.00  
  Purchase #4 $180.56   13.671%   $205.2444   $205.24   $205.25   $205.20  
  Purchase #5 $70.40   9.635%   $77.183   $77.18   $77.20   $77.20  
  Purchase #6 $7.74   3.159%   $7.9845   $7.98   $8.00   $8.00  
  Purchase #7 $51.98   7.740%   $56.0033   $56.00   $56.00   $56.00  
  7 purchase totals = $605.69       $662.4260   $662.42   $662.45   $662.40