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 $220.54   10.635%   $243.9944   $243.99   $244.00   $244.00  
  Purchase #2 $183.52   6.401%   $195.2671   $195.27   $195.25   $195.30  
  Purchase #3 $194.81   6.417%   $207.311   $207.31   $207.30   $207.30  
  Purchase #4 $24.68   11.122%   $27.4249   $27.42   $27.40   $27.40  
  Purchase #5 $165.76   12.684%   $186.785   $186.79   $186.80   $186.80  
  Purchase #6 $29.87   3.684%   $30.9704   $30.97   $30.95   $31.00  
  Purchase #7 $160.93   9.180%   $175.7034   $175.70   $175.70   $175.70  
  7 purchase totals = $980.11       $1,067.4562   $1,067.45   $1,067.40   $1,067.50