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 $52.48   12.774%   $59.1838   $59.18   $59.20   $59.20  
  Purchase #2 $53.29   6.620%   $56.8178   $56.82   $56.80   $56.80  
  Purchase #3 $194.81   3.796%   $202.205   $202.21   $202.20   $202.20  
  Purchase #4 $86.41   4.570%   $90.3589   $90.36   $90.35   $90.40  
  Purchase #5 $85.99   6.786%   $91.8253   $91.83   $91.85   $91.80  
  Purchase #6 $110.43   13.631%   $125.4827   $125.48   $125.50   $125.50  
  Purchase #7 $198.50   4.163%   $206.7636   $206.76   $206.75   $206.80  
  7 purchase totals = $781.91       $832.6371   $832.64   $832.65   $832.70