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 $238.79   11.141%   $265.3936   $265.39   $265.40   $265.40  
  Purchase #2 $230.30   6.638%   $245.5873   $245.59   $245.60   $245.60  
  Purchase #3 $98.28   13.312%   $111.363   $111.36   $111.35   $111.40  
  Purchase #4 $220.72   9.246%   $241.1278   $241.13   $241.15   $241.10  
  Purchase #5 $193.98   9.545%   $212.4954   $212.50   $212.50   $212.50  
  Purchase #6 $113.70   9.260%   $124.2286   $124.23   $124.25   $124.20  
  Purchase #7 $249.33   10.149%   $274.6345   $274.63   $274.65   $274.60  
  7 purchase totals = $1,345.10       $1,474.8302   $1,474.83   $1,474.90   $1,474.80