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 $248.28   4.726%   $260.0137   $260.01   $260.00   $260.00  
  Purchase #2 $11.35   9.226%   $12.3972   $12.40   $12.40   $12.40  
  Purchase #3 $203.56   8.847%   $221.569   $221.57   $221.55   $221.60  
  Purchase #4 $168.68   13.128%   $190.8243   $190.82   $190.80   $190.80  
  Purchase #5 $8.81   8.578%   $9.5657   $9.57   $9.55   $9.60  
  Purchase #6 $210.25   10.693%   $232.732   $232.73   $232.75   $232.70  
  Purchase #7 $88.86   8.268%   $96.2069   $96.21   $96.20   $96.20  
  7 purchase totals = $939.79       $1,023.3088   $1,023.31   $1,023.25   $1,023.30