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 $62.73   8.780%   $68.2377   $68.24   $68.25   $68.20  
  Purchase #2 $176.73   5.535%   $186.512   $186.51   $186.50   $186.50  
  Purchase #3 $75.32   11.534%   $84.0074   $84.01   $84.00   $84.00  
  Purchase #4 $206.28   5.472%   $217.5676   $217.57   $217.55   $217.60  
  Purchase #5 $87.47   5.122%   $91.9502   $91.95   $91.95   $92.00  
  Purchase #6 $233.85   4.798%   $245.0701   $245.07   $245.05   $245.10  
  Purchase #7 $39.29   9.566%   $43.0485   $43.05   $43.05   $43.00  
  7 purchase totals = $881.67       $936.3935   $936.40   $936.35   $936.40