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 $175.42   8.711%   $190.7008   $190.70   $190.70   $190.70  
  Purchase #2 $103.58   5.745%   $109.5307   $109.53   $109.55   $109.50  
  Purchase #3 $125.39   7.607%   $134.9284   $134.93   $134.95   $134.90  
  Purchase #4 $212.93   9.242%   $232.609   $232.61   $232.60   $232.60  
  Purchase #5 $18.25   5.609%   $19.2736   $19.27   $19.25   $19.30  
  Purchase #6 $206.44   3.629%   $213.9317   $213.93   $213.95   $213.90  
  Purchase #7 $119.30   3.668%   $123.6759   $123.68   $123.70   $123.70  
  7 purchase totals = $961.31       $1,024.6501   $1,024.65   $1,024.70   $1,024.60