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 $108.28   6.697%   $115.5315   $115.53   $115.55   $115.50  
  Purchase #2 $145.90   5.116%   $153.3642   $153.36   $153.35   $153.40  
  Purchase #3 $53.87   6.645%   $57.4497   $57.45   $57.45   $57.40  
  Purchase #4 $210.28   4.292%   $219.3052   $219.31   $219.30   $219.30  
  Purchase #5 $120.73   5.674%   $127.5802   $127.58   $127.60   $127.60  
  Purchase #6 $249.41   7.449%   $267.9886   $267.99   $268.00   $268.00  
  Purchase #7 $154.45   12.511%   $173.7732   $173.77   $173.75   $173.80  
  7 purchase totals = $1,042.92       $1,114.9926   $1,114.99   $1,115.00   $1,115.00