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 $232.91   13.165%   $263.5726   $263.57   $263.55   $263.60  
  Purchase #2 $12.80   4.687%   $13.3999   $13.40   $13.40   $13.40  
  Purchase #3 $42.61   9.580%   $46.692   $46.69   $46.70   $46.70  
  Purchase #4 $93.73   13.451%   $106.3376   $106.34   $106.35   $106.30  
  Purchase #5 $75.37   10.250%   $83.0954   $83.10   $83.10   $83.10  
  Purchase #6 $206.33   8.230%   $223.311   $223.31   $223.30   $223.30  
  Purchase #7 $51.75   9.190%   $56.5058   $56.51   $56.50   $56.50  
  7 purchase totals = $715.50       $792.9143   $792.92   $792.90   $792.90