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 $48.79   10.181%   $53.7573   $53.76   $53.75   $53.80  
  Purchase #2 $122.42   3.153%   $126.2799   $126.28   $126.30   $126.30  
  Purchase #3 $95.48   10.179%   $105.1989   $105.20   $105.20   $105.20  
  Purchase #4 $235.69   12.200%   $264.4442   $264.44   $264.45   $264.40  
  Purchase #5 $180.46   3.761%   $187.2471   $187.25   $187.25   $187.20  
  Purchase #6 $122.61   9.776%   $134.5964   $134.60   $134.60   $134.60  
  Purchase #7 $156.76   6.723%   $167.299   $167.30   $167.30   $167.30  
  7 purchase totals = $962.21       $1,038.8228   $1,038.83   $1,038.85   $1,038.80