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 $33.59   13.238%   $38.0366   $38.04   $38.05   $38.00  
  Purchase #2 $194.84   4.286%   $203.1908   $203.19   $203.20   $203.20  
  Purchase #3 $183.91   3.396%   $190.1556   $190.16   $190.15   $190.20  
  Purchase #4 $202.73   3.699%   $210.229   $210.23   $210.25   $210.20  
  Purchase #5 $241.94   5.280%   $254.7144   $254.71   $254.70   $254.70  
  Purchase #6 $110.69   5.283%   $116.5378   $116.54   $116.55   $116.50  
  Purchase #7 $33.97   5.553%   $35.8564   $35.86   $35.85   $35.90  
  7 purchase totals = $1,001.67       $1,048.7206   $1,048.73   $1,048.75   $1,048.70