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 $194.66   7.163%   $208.6035   $208.60   $208.60   $208.60  
  Purchase #2 $52.55   5.163%   $55.2632   $55.26   $55.25   $55.30  
  Purchase #3 $32.60   4.169%   $33.9591   $33.96   $33.95   $34.00  
  Purchase #4 $111.35   13.102%   $125.9391   $125.94   $125.95   $125.90  
  Purchase #5 $233.45   4.505%   $243.9669   $243.97   $243.95   $244.00  
  Purchase #6 $115.72   10.574%   $127.9562   $127.96   $127.95   $128.00  
  Purchase #7 $215.41   12.206%   $241.7029   $241.70   $241.70   $241.70  
  7 purchase totals = $955.74       $1,037.3909   $1,037.39   $1,037.35   $1,037.50