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 $60.95   4.409%   $63.6373   $63.64   $63.65   $63.60  
  Purchase #2 $54.85   3.132%   $56.5679   $56.57   $56.55   $56.60  
  Purchase #3 $106.34   11.304%   $118.3607   $118.36   $118.35   $118.40  
  Purchase #4 $24.67   10.138%   $27.171   $27.17   $27.15   $27.20  
  Purchase #5 $164.91   12.312%   $185.2137   $185.21   $185.20   $185.20  
  Purchase #6 $207.46   3.797%   $215.3373   $215.34   $215.35   $215.30  
  Purchase #7 $173.77   5.179%   $182.7695   $182.77   $182.75   $182.80  
  7 purchase totals = $792.95       $849.0574   $849.06   $849.00   $849.10