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 $53.46   7.753%   $57.6048   $57.60   $57.60   $57.60  
  Purchase #2 $79.97   3.220%   $82.545   $82.55   $82.55   $82.50  
  Purchase #3 $155.53   5.704%   $164.4014   $164.40   $164.40   $164.40  
  Purchase #4 $158.32   4.417%   $165.313   $165.31   $165.30   $165.30  
  Purchase #5 $207.63   12.271%   $233.1083   $233.11   $233.10   $233.10  
  Purchase #6 $234.90   7.285%   $252.0125   $252.01   $252.00   $252.00  
  Purchase #7 $54.55   4.155%   $56.8166   $56.82   $56.80   $56.80  
  7 purchase totals = $944.36       $1,011.8016   $1,011.80   $1,011.75   $1,011.70