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 $234.29   13.558%   $266.055   $266.06   $266.05   $266.10  
  Purchase #2 $34.76   11.501%   $38.7577   $38.76   $38.75   $38.80  
  Purchase #3 $214.55   12.359%   $241.0662   $241.07   $241.05   $241.10  
  Purchase #4 $154.57   5.628%   $163.2692   $163.27   $163.25   $163.30  
  Purchase #5 $209.96   3.842%   $218.0267   $218.03   $218.05   $218.00  
  Purchase #6 $213.51   5.871%   $226.0452   $226.05   $226.05   $226.00  
  Purchase #7 $239.31   11.383%   $266.5507   $266.55   $266.55   $266.60  
  7 purchase totals = $1,300.95       $1,419.7707   $1,419.79   $1,419.75   $1,419.90