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 $47.65   10.276%   $52.5465   $52.55   $52.55   $52.50  
  Purchase #2 $101.82   12.238%   $114.2807   $114.28   $114.30   $114.30  
  Purchase #3 $101.80   3.556%   $105.42   $105.42   $105.40   $105.40  
  Purchase #4 $25.72   12.245%   $28.8694   $28.87   $28.85   $28.90  
  Purchase #5 $232.79   6.201%   $247.2253   $247.23   $247.25   $247.20  
  Purchase #6 $119.35   12.524%   $134.2974   $134.30   $134.30   $134.30  
  Purchase #7 $161.59   5.366%   $170.2609   $170.26   $170.25   $170.30  
  7 purchase totals = $790.72       $852.9002   $852.91   $852.90   $852.90