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 $145.47   4.151%   $151.5085   $151.51   $151.50   $151.50  
  Purchase #2 $67.25   10.683%   $74.4343   $74.43   $74.45   $74.40  
  Purchase #3 $73.47   4.378%   $76.6865   $76.69   $76.70   $76.70  
  Purchase #4 $223.44   5.726%   $236.2342   $236.23   $236.25   $236.20  
  Purchase #5 $198.51   4.465%   $207.3735   $207.37   $207.35   $207.40  
  Purchase #6 $184.75   10.488%   $204.1266   $204.13   $204.15   $204.10  
  Purchase #7 $89.86   3.745%   $93.2253   $93.23   $93.25   $93.20  
  7 purchase totals = $982.75       $1,043.5889   $1,043.59   $1,043.65   $1,043.50