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 $31.90   11.628%   $35.6093   $35.61   $35.60   $35.60  
  Purchase #2 $241.92   7.370%   $259.7495   $259.75   $259.75   $259.70  
  Purchase #3 $246.67   3.853%   $256.1742   $256.17   $256.15   $256.20  
  Purchase #4 $24.58   7.271%   $26.3672   $26.37   $26.35   $26.40  
  Purchase #5 $16.58   8.638%   $18.0122   $18.01   $18.00   $18.00  
  Purchase #6 $230.60   6.763%   $246.1955   $246.20   $246.20   $246.20  
  Purchase #7 $181.32   3.424%   $187.5284   $187.53   $187.55   $187.50  
  7 purchase totals = $973.57       $1,029.6363   $1,029.64   $1,029.60   $1,029.60