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 $44.58   13.621%   $50.6522   $50.65   $50.65   $50.70  
  Purchase #2 $86.93   11.182%   $96.6505   $96.65   $96.65   $96.70  
  Purchase #3 $109.73   8.172%   $118.6971   $118.70   $118.70   $118.70  
  Purchase #4 $25.96   13.507%   $29.4664   $29.47   $29.45   $29.50  
  Purchase #5 $223.88   9.500%   $245.1486   $245.15   $245.15   $245.10  
  Purchase #6 $135.80   7.479%   $145.9565   $145.96   $145.95   $146.00  
  Purchase #7 $57.41   9.105%   $62.6372   $62.64   $62.65   $62.60  
  7 purchase totals = $684.29       $749.2085   $749.22   $749.20   $749.30