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 $96.95   12.760%   $109.3208   $109.32   $109.30   $109.30  
  Purchase #2 $174.75   13.221%   $197.8537   $197.85   $197.85   $197.90  
  Purchase #3 $113.73   3.342%   $117.5309   $117.53   $117.55   $117.50  
  Purchase #4 $24.73   13.187%   $27.9911   $27.99   $28.00   $28.00  
  Purchase #5 $153.71   8.842%   $167.301   $167.30   $167.30   $167.30  
  Purchase #6 $13.75   12.657%   $15.4903   $15.49   $15.50   $15.50  
  Purchase #7 $139.43   8.551%   $151.3527   $151.35   $151.35   $151.40  
  7 purchase totals = $717.05       $786.8405   $786.83   $786.85   $786.90