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 $221.40   12.104%   $248.1983   $248.20   $248.20   $248.20  
  Purchase #2 $168.55   4.803%   $176.6455   $176.65   $176.65   $176.60  
  Purchase #3 $232.67   13.494%   $264.0665   $264.07   $264.05   $264.10  
  Purchase #4 $231.75   4.115%   $241.2865   $241.29   $241.30   $241.30  
  Purchase #5 $23.91   8.828%   $26.0208   $26.02   $26.00   $26.00  
  Purchase #6 $28.48   4.521%   $29.7676   $29.77   $29.75   $29.80  
  Purchase #7 $166.31   9.127%   $181.4891   $181.49   $181.50   $181.50  
  7 purchase totals = $1,073.07       $1,167.4743   $1,167.49   $1,167.45   $1,167.50