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 $215.25   13.177%   $243.6135   $243.61   $243.60   $243.60  
  Purchase #2 $23.78   7.483%   $25.5595   $25.56   $25.55   $25.60  
  Purchase #3 $197.89   7.841%   $213.4066   $213.41   $213.40   $213.40  
  Purchase #4 $118.25   10.153%   $130.2559   $130.26   $130.25   $130.30  
  Purchase #5 $170.60   3.156%   $175.9841   $175.98   $176.00   $176.00  
  Purchase #6 $60.97   4.250%   $63.5612   $63.56   $63.55   $63.60  
  Purchase #7 $176.91   12.127%   $198.3639   $198.36   $198.35   $198.40  
  7 purchase totals = $963.65       $1,050.7447   $1,050.74   $1,050.70   $1,050.90