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 $103.57   11.539%   $115.5209   $115.52   $115.50   $115.50  
  Purchase #2 $223.81   10.140%   $246.5043   $246.50   $246.50   $246.50  
  Purchase #3 $208.83   3.623%   $216.3959   $216.40   $216.40   $216.40  
  Purchase #4 $22.55   3.388%   $23.314   $23.31   $23.30   $23.30  
  Purchase #5 $118.53   3.768%   $122.9962   $123.00   $123.00   $123.00  
  Purchase #6 $112.93   11.498%   $125.9147   $125.91   $125.90   $125.90  
  Purchase #7 $157.98   3.667%   $163.7731   $163.77   $163.75   $163.80  
  7 purchase totals = $948.20       $1,014.4191   $1,014.41   $1,014.35   $1,014.40