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 $185.96   8.673%   $202.0883   $202.09   $202.10   $202.10  
  Purchase #2 $68.66   3.258%   $70.8969   $70.90   $70.90   $70.90  
  Purchase #3 $117.31   7.402%   $125.9933   $125.99   $126.00   $126.00  
  Purchase #4 $41.54   5.416%   $43.7898   $43.79   $43.80   $43.80  
  Purchase #5 $59.53   5.156%   $62.5994   $62.60   $62.60   $62.60  
  Purchase #6 $90.79   13.534%   $103.0775   $103.08   $103.10   $103.10  
  Purchase #7 $107.76   9.156%   $117.6265   $117.63   $117.65   $117.60  
  7 purchase totals = $671.55       $726.0717   $726.08   $726.15   $726.10