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 $63.53   6.615%   $67.7325   $67.73   $67.75   $67.70  
  Purchase #2 $222.70   10.124%   $245.2461   $245.25   $245.25   $245.20  
  Purchase #3 $60.35   6.673%   $64.3772   $64.38   $64.40   $64.40  
  Purchase #4 $205.29   9.718%   $225.2401   $225.24   $225.25   $225.20  
  Purchase #5 $127.97   10.383%   $141.2571   $141.26   $141.25   $141.30  
  Purchase #6 $29.59   4.340%   $30.8742   $30.87   $30.85   $30.90  
  Purchase #7 $225.94   7.564%   $243.0301   $243.03   $243.05   $243.00  
  7 purchase totals = $935.37       $1,017.7573   $1,017.76   $1,017.80   $1,017.70