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 $71.84   7.658%   $77.3415   $77.34   $77.35   $77.30  
  Purchase #2 $10.73   6.391%   $11.4158   $11.42   $11.40   $11.40  
  Purchase #3 $174.43   7.826%   $188.0809   $188.08   $188.10   $188.10  
  Purchase #4 $119.71   4.154%   $124.6828   $124.68   $124.70   $124.70  
  Purchase #5 $186.27   3.366%   $192.5398   $192.54   $192.55   $192.50  
  Purchase #6 $135.83   11.370%   $151.2739   $151.27   $151.25   $151.30  
  Purchase #7 $49.40   7.265%   $52.9889   $52.99   $53.00   $53.00  
  7 purchase totals = $748.21       $798.3236   $798.32   $798.35   $798.30