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 $36.41   7.366%   $39.092   $39.09   $39.10   $39.10  
  Purchase #2 $96.87   6.455%   $103.123   $103.12   $103.10   $103.10  
  Purchase #3 $6.62   7.394%   $7.1095   $7.11   $7.10   $7.10  
  Purchase #4 $9.26   7.841%   $9.9861   $9.99   $10.00   $10.00  
  Purchase #5 $133.72   3.789%   $138.7867   $138.79   $138.80   $138.80  
  Purchase #6 $141.33   4.306%   $147.4157   $147.42   $147.40   $147.40  
  Purchase #7 $241.54   13.394%   $273.8919   $273.89   $273.90   $273.90  
  7 purchase totals = $665.75       $719.4049   $719.41   $719.40   $719.40