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 $42.76   4.655%   $44.7505   $44.75   $44.75   $44.80  
  Purchase #2 $85.96   13.610%   $97.6592   $97.66   $97.65   $97.70  
  Purchase #3 $192.73   10.347%   $212.6718   $212.67   $212.65   $212.70  
  Purchase #4 $187.66   9.490%   $205.4689   $205.47   $205.45   $205.50  
  Purchase #5 $171.92   11.106%   $191.0134   $191.01   $191.00   $191.00  
  Purchase #6 $123.82   12.182%   $138.9038   $138.90   $138.90   $138.90  
  Purchase #7 $57.65   7.522%   $61.9864   $61.99   $62.00   $62.00  
  7 purchase totals = $862.50       $952.4540   $952.45   $952.40   $952.60