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 $38.76   11.141%   $43.0783   $43.08   $43.10   $43.10  
  Purchase #2 $38.92   6.721%   $41.5358   $41.54   $41.55   $41.50  
  Purchase #3 $122.80   3.694%   $127.3362   $127.34   $127.35   $127.30  
  Purchase #4 $99.91   6.631%   $106.535   $106.54   $106.55   $106.50  
  Purchase #5 $200.25   11.361%   $223.0004   $223.00   $223.00   $223.00  
  Purchase #6 $235.44   7.322%   $252.6789   $252.68   $252.70   $252.70  
  Purchase #7 $123.94   9.516%   $135.7341   $135.73   $135.75   $135.70  
  7 purchase totals = $860.02       $929.8987   $929.91   $930.00   $929.80