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 $183.58   12.159%   $205.9015   $205.90   $205.90   $205.90  
  Purchase #2 $21.73   5.118%   $22.8421   $22.84   $22.85   $22.80  
  Purchase #3 $39.49   13.225%   $44.7126   $44.71   $44.70   $44.70  
  Purchase #4 $50.78   12.867%   $57.3139   $57.31   $57.30   $57.30  
  Purchase #5 $138.83   7.524%   $149.2756   $149.28   $149.30   $149.30  
  Purchase #6 $200.59   11.697%   $224.053   $224.05   $224.05   $224.10  
  Purchase #7 $68.71   12.388%   $77.2218   $77.22   $77.20   $77.20  
  7 purchase totals = $703.71       $781.3205   $781.31   $781.30   $781.30