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 $226.94   12.215%   $254.6607   $254.66   $254.65   $254.70  
  Purchase #2 $167.91   5.360%   $176.91   $176.91   $176.90   $176.90  
  Purchase #3 $105.72   10.463%   $116.7815   $116.78   $116.80   $116.80  
  Purchase #4 $210.98   13.448%   $239.3526   $239.35   $239.35   $239.40  
  Purchase #5 $9.49   13.203%   $10.743   $10.74   $10.75   $10.70  
  Purchase #6 $25.44   12.441%   $28.605   $28.61   $28.60   $28.60  
  Purchase #7 $227.71   12.495%   $256.1624   $256.16   $256.15   $256.20  
  7 purchase totals = $974.19       $1,083.2152   $1,083.21   $1,083.20   $1,083.30