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 $202.51   5.272%   $213.1863   $213.19   $213.20   $213.20  
  Purchase #2 $53.47   3.399%   $55.2874   $55.29   $55.30   $55.30  
  Purchase #3 $241.47   7.176%   $258.7979   $258.80   $258.80   $258.80  
  Purchase #4 $45.91   8.705%   $49.9065   $49.91   $49.90   $49.90  
  Purchase #5 $196.75   11.569%   $219.512   $219.51   $219.50   $219.50  
  Purchase #6 $232.69   8.757%   $253.0667   $253.07   $253.05   $253.10  
  Purchase #7 $59.64   12.847%   $67.302   $67.30   $67.30   $67.30  
  7 purchase totals = $1,032.44       $1,117.0588   $1,117.07   $1,117.05   $1,117.10