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 $228.59   3.456%   $236.4901   $236.49   $236.50   $236.50  
  Purchase #2 $99.39   4.310%   $103.6737   $103.67   $103.65   $103.70  
  Purchase #3 $91.67   4.326%   $95.6356   $95.64   $95.65   $95.60  
  Purchase #4 $203.75   4.666%   $213.257   $213.26   $213.25   $213.30  
  Purchase #5 $178.63   3.320%   $184.5605   $184.56   $184.55   $184.60  
  Purchase #6 $250.59   3.297%   $258.852   $258.85   $258.85   $258.90  
  Purchase #7 $122.56   11.600%   $136.777   $136.78   $136.80   $136.80  
  7 purchase totals = $1,175.18       $1,229.2459   $1,229.25   $1,229.25   $1,229.40