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 $201.43   8.671%   $218.896   $218.90   $218.90   $218.90  
  Purchase #2 $125.43   11.157%   $139.4242   $139.42   $139.40   $139.40  
  Purchase #3 $39.51   10.731%   $43.7498   $43.75   $43.75   $43.70  
  Purchase #4 $161.91   8.295%   $175.3404   $175.34   $175.35   $175.30  
  Purchase #5 $172.43   13.843%   $196.2995   $196.30   $196.30   $196.30  
  Purchase #6 $226.35   8.670%   $245.9745   $245.97   $245.95   $246.00  
  Purchase #7 $24.60   12.567%   $27.6915   $27.69   $27.70   $27.70  
  7 purchase totals = $951.66       $1,047.3759   $1,047.37   $1,047.35   $1,047.30