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 $60.53   12.623%   $68.1707   $68.17   $68.15   $68.20  
  Purchase #2 $46.83   4.486%   $48.9308   $48.93   $48.95   $48.90  
  Purchase #3 $75.44   4.800%   $79.0611   $79.06   $79.05   $79.10  
  Purchase #4 $105.72   7.675%   $113.834   $113.83   $113.85   $113.80  
  Purchase #5 $238.40   6.558%   $254.0343   $254.03   $254.05   $254.00  
  Purchase #6 $124.47   3.746%   $129.1326   $129.13   $129.15   $129.10  
  Purchase #7 $111.57   12.599%   $125.6267   $125.63   $125.65   $125.60  
  7 purchase totals = $762.96       $818.7902   $818.78   $818.85   $818.70