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 $185.83   8.519%   $201.6609   $201.66   $201.65   $201.70  
  Purchase #2 $57.28   7.703%   $61.6923   $61.69   $61.70   $61.70  
  Purchase #3 $84.99   11.851%   $95.0622   $95.06   $95.05   $95.10  
  Purchase #4 $167.94   12.508%   $188.9459   $188.95   $188.95   $188.90  
  Purchase #5 $83.51   12.463%   $93.9179   $93.92   $93.90   $93.90  
  Purchase #6 $151.92   5.661%   $160.5202   $160.52   $160.50   $160.50  
  Purchase #7 $208.27   6.117%   $221.0099   $221.01   $221.00   $221.00  
  7 purchase totals = $939.74       $1,022.8093   $1,022.81   $1,022.75   $1,022.80