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 $54.31   6.702%   $57.9499   $57.95   $57.95   $57.90  
  Purchase #2 $134.91   12.163%   $151.3191   $151.32   $151.30   $151.30  
  Purchase #3 $68.33   11.412%   $76.1278   $76.13   $76.15   $76.10  
  Purchase #4 $100.89   11.490%   $112.4823   $112.48   $112.50   $112.50  
  Purchase #5 $206.96   11.141%   $230.0174   $230.02   $230.00   $230.00  
  Purchase #6 $230.88   12.478%   $259.6892   $259.69   $259.70   $259.70  
  Purchase #7 $243.82   6.787%   $260.3681   $260.37   $260.35   $260.40  
  7 purchase totals = $1,040.10       $1,147.9538   $1,147.96   $1,147.95   $1,147.90