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 $68.87   11.113%   $76.5235   $76.52   $76.50   $76.50  
  Purchase #2 $153.46   6.781%   $163.8661   $163.87   $163.85   $163.90  
  Purchase #3 $73.84   4.117%   $76.88   $76.88   $76.90   $76.90  
  Purchase #4 $185.25   4.658%   $193.8789   $193.88   $193.90   $193.90  
  Purchase #5 $135.99   10.348%   $150.0622   $150.06   $150.05   $150.10  
  Purchase #6 $244.50   5.520%   $257.9964   $258.00   $258.00   $258.00  
  Purchase #7 $136.66   5.612%   $144.3294   $144.33   $144.35   $144.30  
  7 purchase totals = $998.57       $1,063.5365   $1,063.54   $1,063.55   $1,063.60