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 $119.51   6.444%   $127.2112   $127.21   $127.20   $127.20  
  Purchase #2 $220.80   8.687%   $239.9809   $239.98   $240.00   $240.00  
  Purchase #3 $39.25   11.331%   $43.6974   $43.70   $43.70   $43.70  
  Purchase #4 $100.77   4.692%   $105.4981   $105.50   $105.50   $105.50  
  Purchase #5 $109.29   6.795%   $116.7163   $116.72   $116.70   $116.70  
  Purchase #6 $68.31   10.646%   $75.5823   $75.58   $75.60   $75.60  
  Purchase #7 $225.60   8.602%   $245.0061   $245.01   $245.00   $245.00  
  7 purchase totals = $883.53       $953.6923   $953.70   $953.70   $953.70