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 $237.66   12.682%   $267.8   $267.80   $267.80   $267.80  
  Purchase #2 $33.67   3.745%   $34.9309   $34.93   $34.95   $34.90  
  Purchase #3 $102.63   10.329%   $113.2307   $113.23   $113.25   $113.20  
  Purchase #4 $224.66   6.315%   $238.8473   $238.85   $238.85   $238.80  
  Purchase #5 $105.45   9.752%   $115.7335   $115.73   $115.75   $115.70  
  Purchase #6 $111.50   8.451%   $120.9229   $120.92   $120.90   $120.90  
  Purchase #7 $206.78   6.172%   $219.5425   $219.54   $219.55   $219.50  
  7 purchase totals = $1,022.35       $1,111.0078   $1,111.00   $1,111.05   $1,110.80