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 $73.77   11.549%   $82.2897   $82.29   $82.30   $82.30  
  Purchase #2 $154.44   12.481%   $173.7157   $173.72   $173.70   $173.70  
  Purchase #3 $66.32   12.147%   $74.3759   $74.38   $74.40   $74.40  
  Purchase #4 $160.67   4.678%   $168.1861   $168.19   $168.20   $168.20  
  Purchase #5 $235.89   6.855%   $252.0603   $252.06   $252.05   $252.10  
  Purchase #6 $70.79   12.835%   $79.8759   $79.88   $79.90   $79.90  
  Purchase #7 $177.99   3.254%   $183.7818   $183.78   $183.80   $183.80  
  7 purchase totals = $939.87       $1,014.2854   $1,014.30   $1,014.35   $1,014.40