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 $52.77   12.260%   $59.2396   $59.24   $59.25   $59.20  
  Purchase #2 $222.99   12.691%   $251.2897   $251.29   $251.30   $251.30  
  Purchase #3 $202.78   7.872%   $218.7428   $218.74   $218.75   $218.70  
  Purchase #4 $244.75   3.241%   $252.6823   $252.68   $252.70   $252.70  
  Purchase #5 $91.41   5.626%   $96.5527   $96.55   $96.55   $96.60  
  Purchase #6 $203.42   3.570%   $210.6821   $210.68   $210.70   $210.70  
  Purchase #7 $157.35   7.592%   $169.296   $169.30   $169.30   $169.30  
  7 purchase totals = $1,175.47       $1,258.4852   $1,258.48   $1,258.55   $1,258.50