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 $233.53   5.661%   $246.7501   $246.75   $246.75   $246.80  
  Purchase #2 $184.28   4.584%   $192.7274   $192.73   $192.75   $192.70  
  Purchase #3 $125.43   6.685%   $133.815   $133.82   $133.80   $133.80  
  Purchase #4 $47.36   4.647%   $49.5608   $49.56   $49.55   $49.60  
  Purchase #5 $114.33   3.782%   $118.654   $118.65   $118.65   $118.70  
  Purchase #6 $20.47   5.124%   $21.5189   $21.52   $21.50   $21.50  
  Purchase #7 $51.56   9.183%   $56.2948   $56.29   $56.30   $56.30  
  7 purchase totals = $776.96       $819.3210   $819.32   $819.30   $819.40