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 $207.48   7.319%   $222.6655   $222.67   $222.65   $222.70  
  Purchase #2 $9.35   10.813%   $10.361   $10.36   $10.35   $10.40  
  Purchase #3 $36.43   7.241%   $39.0679   $39.07   $39.05   $39.10  
  Purchase #4 $222.41   8.645%   $241.6373   $241.64   $241.65   $241.60  
  Purchase #5 $129.32   8.807%   $140.7092   $140.71   $140.70   $140.70  
  Purchase #6 $11.62   5.301%   $12.236   $12.24   $12.25   $12.20  
  Purchase #7 $96.76   13.489%   $109.812   $109.81   $109.80   $109.80  
  7 purchase totals = $713.37       $776.4889   $776.50   $776.45   $776.50