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 $236.42   13.328%   $267.9301   $267.93   $267.95   $267.90  
  Purchase #2 $226.34   6.343%   $240.6967   $240.70   $240.70   $240.70  
  Purchase #3 $59.81   5.704%   $63.2216   $63.22   $63.20   $63.20  
  Purchase #4 $237.81   11.809%   $265.893   $265.89   $265.90   $265.90  
  Purchase #5 $235.27   5.373%   $247.9111   $247.91   $247.90   $247.90  
  Purchase #6 $100.92   12.472%   $113.5067   $113.51   $113.50   $113.50  
  Purchase #7 $21.32   8.675%   $23.1695   $23.17   $23.15   $23.20  
  7 purchase totals = $1,117.89       $1,222.3287   $1,222.33   $1,222.30   $1,222.30