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 $94.78   9.202%   $103.5017   $103.50   $103.50   $103.50  
  Purchase #2 $173.90   11.855%   $194.5158   $194.52   $194.50   $194.50  
  Purchase #3 $209.64   9.131%   $228.7822   $228.78   $228.80   $228.80  
  Purchase #4 $24.36   7.765%   $26.2516   $26.25   $26.25   $26.30  
  Purchase #5 $18.77   5.799%   $19.8585   $19.86   $19.85   $19.90  
  Purchase #6 $6.28   8.311%   $6.8019   $6.80   $6.80   $6.80  
  Purchase #7 $91.55   8.306%   $99.1541   $99.15   $99.15   $99.20  
  7 purchase totals = $619.28       $678.8658   $678.86   $678.85   $679.00