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 $66.59   3.508%   $68.926   $68.93   $68.95   $68.90  
  Purchase #2 $205.30   6.667%   $218.9874   $218.99   $219.00   $219.00  
  Purchase #3 $21.70   5.826%   $22.9642   $22.96   $22.95   $23.00  
  Purchase #4 $103.52   8.621%   $112.4445   $112.44   $112.45   $112.40  
  Purchase #5 $161.97   8.259%   $175.3471   $175.35   $175.35   $175.30  
  Purchase #6 $112.71   12.577%   $126.8855   $126.89   $126.90   $126.90  
  Purchase #7 $79.65   8.487%   $86.4099   $86.41   $86.40   $86.40  
  7 purchase totals = $751.44       $811.9646   $811.97   $812.00   $811.90