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 $176.44   3.728%   $183.0177   $183.02   $183.00   $183.00  
  Purchase #2 $222.91   9.252%   $243.5336   $243.53   $243.55   $243.50  
  Purchase #3 $19.93   8.869%   $21.6976   $21.70   $21.70   $21.70  
  Purchase #4 $26.83   10.715%   $29.7048   $29.70   $29.70   $29.70  
  Purchase #5 $84.76   10.106%   $93.3258   $93.33   $93.35   $93.30  
  Purchase #6 $58.73   12.745%   $66.2151   $66.22   $66.20   $66.20  
  Purchase #7 $118.52   3.352%   $122.4928   $122.49   $122.50   $122.50  
  7 purchase totals = $708.12       $759.9874   $759.99   $760.00   $759.90