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 $234.67   10.867%   $260.1716   $260.17   $260.15   $260.20  
  Purchase #2 $151.74   5.220%   $159.6608   $159.66   $159.65   $159.70  
  Purchase #3 $207.99   8.690%   $226.0643   $226.06   $226.05   $226.10  
  Purchase #4 $131.43   7.339%   $141.0756   $141.08   $141.10   $141.10  
  Purchase #5 $217.40   11.270%   $241.901   $241.90   $241.90   $241.90  
  Purchase #6 $76.57   4.211%   $79.7944   $79.79   $79.80   $79.80  
  Purchase #7 $79.50   4.245%   $82.8748   $82.87   $82.85   $82.90  
  7 purchase totals = $1,099.30       $1,191.5425   $1,191.53   $1,191.50   $1,191.70