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 $226.85   9.284%   $247.9108   $247.91   $247.90   $247.90  
  Purchase #2 $162.54   7.564%   $174.8345   $174.83   $174.85   $174.80  
  Purchase #3 $48.87   5.183%   $51.4029   $51.40   $51.40   $51.40  
  Purchase #4 $18.27   5.170%   $19.2146   $19.21   $19.20   $19.20  
  Purchase #5 $172.25   3.718%   $178.6543   $178.65   $178.65   $178.70  
  Purchase #6 $117.53   3.343%   $121.459   $121.46   $121.45   $121.50  
  Purchase #7 $7.48   7.227%   $8.0206   $8.02   $8.00   $8.00  
  7 purchase totals = $753.79       $801.4967   $801.48   $801.45   $801.50