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 $62.43   4.427%   $65.1938   $65.19   $65.20   $65.20  
  Purchase #2 $225.46   11.481%   $251.3451   $251.35   $251.35   $251.30  
  Purchase #3 $224.81   7.866%   $242.4936   $242.49   $242.50   $242.50  
  Purchase #4 $108.88   12.529%   $122.5216   $122.52   $122.50   $122.50  
  Purchase #5 $157.93   3.447%   $163.3738   $163.37   $163.35   $163.40  
  Purchase #6 $199.73   13.280%   $226.2541   $226.25   $226.25   $226.30  
  Purchase #7 $217.80   6.464%   $231.8786   $231.88   $231.90   $231.90  
  7 purchase totals = $1,197.04       $1,303.0606   $1,303.05   $1,303.05   $1,303.10