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 $218.98   10.383%   $241.7167   $241.72   $241.70   $241.70  
  Purchase #2 $127.62   5.293%   $134.3749   $134.37   $134.35   $134.40  
  Purchase #3 $131.55   7.401%   $141.286   $141.29   $141.30   $141.30  
  Purchase #4 $202.53   5.532%   $213.734   $213.73   $213.75   $213.70  
  Purchase #5 $172.56   3.444%   $178.503   $178.50   $178.50   $178.50  
  Purchase #6 $176.59   7.817%   $190.394   $190.39   $190.40   $190.40  
  Purchase #7 $7.67   8.753%   $8.3414   $8.34   $8.35   $8.30  
  7 purchase totals = $1,037.50       $1,108.3500   $1,108.34   $1,108.35   $1,108.30