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 $112.50   12.459%   $126.5164   $126.52   $126.50   $126.50  
  Purchase #2 $200.35   5.671%   $211.7118   $211.71   $211.70   $211.70  
  Purchase #3 $151.31   3.160%   $156.0914   $156.09   $156.10   $156.10  
  Purchase #4 $23.46   10.186%   $25.8496   $25.85   $25.85   $25.80  
  Purchase #5 $236.93   12.534%   $266.6268   $266.63   $266.65   $266.60  
  Purchase #6 $114.53   4.663%   $119.8705   $119.87   $119.85   $119.90  
  Purchase #7 $39.65   5.700%   $41.9101   $41.91   $41.90   $41.90  
  7 purchase totals = $878.73       $948.5766   $948.58   $948.55   $948.50