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 $151.96   7.621%   $163.5409   $163.54   $163.55   $163.50  
  Purchase #2 $235.52   8.436%   $255.3885   $255.39   $255.40   $255.40  
  Purchase #3 $84.68   5.313%   $89.179   $89.18   $89.20   $89.20  
  Purchase #4 $236.77   4.704%   $247.9077   $247.91   $247.90   $247.90  
  Purchase #5 $57.52   4.260%   $59.9704   $59.97   $59.95   $60.00  
  Purchase #6 $54.36   11.364%   $60.5375   $60.54   $60.55   $60.50  
  Purchase #7 $67.84   10.419%   $74.9082   $74.91   $74.90   $74.90  
  7 purchase totals = $888.65       $951.4322   $951.44   $951.45   $951.40