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 $233.44   5.361%   $245.9547   $245.95   $245.95   $246.00  
  Purchase #2 $40.36   7.176%   $43.2562   $43.26   $43.25   $43.30  
  Purchase #3 $208.76   4.740%   $218.6552   $218.66   $218.65   $218.70  
  Purchase #4 $56.88   4.840%   $59.633   $59.63   $59.65   $59.60  
  Purchase #5 $165.45   12.698%   $186.4588   $186.46   $186.45   $186.50  
  Purchase #6 $12.68   4.777%   $13.2857   $13.29   $13.30   $13.30  
  Purchase #7 $205.98   6.300%   $218.9567   $218.96   $218.95   $219.00  
  7 purchase totals = $923.55       $986.2003   $986.21   $986.20   $986.40