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 $196.52   13.732%   $223.5061   $223.51   $223.50   $223.50  
  Purchase #2 $245.77   6.279%   $261.2019   $261.20   $261.20   $261.20  
  Purchase #3 $237.90   8.841%   $258.9327   $258.93   $258.95   $258.90  
  Purchase #4 $38.99   12.266%   $43.7725   $43.77   $43.75   $43.80  
  Purchase #5 $83.31   5.473%   $87.8696   $87.87   $87.85   $87.90  
  Purchase #6 $82.27   10.746%   $91.1107   $91.11   $91.10   $91.10  
  Purchase #7 $249.54   4.742%   $261.3732   $261.37   $261.35   $261.40  
  7 purchase totals = $1,134.30       $1,227.7667   $1,227.76   $1,227.70   $1,227.80