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 $53.96   4.793%   $56.5463   $56.55   $56.55   $56.50  
  Purchase #2 $232.73   6.208%   $247.1779   $247.18   $247.20   $247.20  
  Purchase #3 $157.28   10.289%   $173.4625   $173.46   $173.45   $173.50  
  Purchase #4 $116.35   13.569%   $132.1375   $132.14   $132.15   $132.10  
  Purchase #5 $181.58   8.515%   $197.0415   $197.04   $197.05   $197.00  
  Purchase #6 $121.66   4.515%   $127.1529   $127.15   $127.15   $127.20  
  Purchase #7 $165.68   5.194%   $174.2854   $174.29   $174.30   $174.30  
  7 purchase totals = $1,029.24       $1,107.8040   $1,107.81   $1,107.85   $1,107.80