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 $92.96   5.150%   $97.7474   $97.75   $97.75   $97.70  
  Purchase #2 $14.79   3.852%   $15.3597   $15.36   $15.35   $15.40  
  Purchase #3 $127.25   4.751%   $133.2956   $133.30   $133.30   $133.30  
  Purchase #4 $98.55   8.449%   $106.8765   $106.88   $106.90   $106.90  
  Purchase #5 $212.76   12.791%   $239.9741   $239.97   $239.95   $240.00  
  Purchase #6 $16.32   3.789%   $16.9384   $16.94   $16.95   $16.90  
  Purchase #7 $200.60   8.200%   $217.0492   $217.05   $217.05   $217.00  
  7 purchase totals = $763.23       $827.2409   $827.25   $827.25   $827.20