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 $199.99   7.725%   $215.4392   $215.44   $215.45   $215.40  
  Purchase #2 $221.67   3.748%   $229.9782   $229.98   $230.00   $230.00  
  Purchase #3 $201.46   13.558%   $228.7739   $228.77   $228.75   $228.80  
  Purchase #4 $5.59   9.278%   $6.1086   $6.11   $6.10   $6.10  
  Purchase #5 $82.56   11.731%   $92.2451   $92.25   $92.25   $92.20  
  Purchase #6 $50.98   10.797%   $56.4843   $56.48   $56.50   $56.50  
  Purchase #7 $237.91   8.249%   $257.5352   $257.54   $257.55   $257.50  
  7 purchase totals = $1,000.16       $1,086.5645   $1,086.57   $1,086.60   $1,086.50