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 $10.82   8.528%   $11.7427   $11.74   $11.75   $11.70  
  Purchase #2 $63.61   8.422%   $68.9672   $68.97   $68.95   $69.00  
  Purchase #3 $222.40   13.312%   $252.0059   $252.01   $252.00   $252.00  
  Purchase #4 $81.61   3.798%   $84.7095   $84.71   $84.70   $84.70  
  Purchase #5 $242.58   3.546%   $251.1819   $251.18   $251.20   $251.20  
  Purchase #6 $59.66   12.763%   $67.2744   $67.27   $67.25   $67.30  
  Purchase #7 $23.34   4.417%   $24.3709   $24.37   $24.35   $24.40  
  7 purchase totals = $704.02       $760.2525   $760.25   $760.20   $760.30