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 $161.41   8.529%   $175.1767   $175.18   $175.20   $175.20  
  Purchase #2 $202.94   3.233%   $209.5011   $209.50   $209.50   $209.50  
  Purchase #3 $195.44   11.850%   $218.5996   $218.60   $218.60   $218.60  
  Purchase #4 $87.68   11.303%   $97.5905   $97.59   $97.60   $97.60  
  Purchase #5 $35.27   5.585%   $37.2398   $37.24   $37.25   $37.20  
  Purchase #6 $5.58   6.798%   $5.9593   $5.96   $5.95   $6.00  
  Purchase #7 $72.42   13.346%   $82.0852   $82.09   $82.10   $82.10  
  7 purchase totals = $760.74       $826.1522   $826.16   $826.20   $826.20