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 $7.67   10.353%   $8.4641   $8.46   $8.45   $8.50  
  Purchase #2 $20.48   4.515%   $21.4047   $21.40   $21.40   $21.40  
  Purchase #3 $120.62   8.700%   $131.1139   $131.11   $131.10   $131.10  
  Purchase #4 $12.37   3.677%   $12.8248   $12.82   $12.80   $12.80  
  Purchase #5 $80.55   5.561%   $85.0294   $85.03   $85.05   $85.00  
  Purchase #6 $91.84   4.347%   $95.8323   $95.83   $95.85   $95.80  
  Purchase #7 $73.39   7.796%   $79.1115   $79.11   $79.10   $79.10  
  7 purchase totals = $406.92       $433.7807   $433.76   $433.75   $433.70