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 $163.73   12.496%   $184.1897   $184.19   $184.20   $184.20  
  Purchase #2 $127.96   13.700%   $145.4905   $145.49   $145.50   $145.50  
  Purchase #3 $160.35   13.269%   $181.6268   $181.63   $181.65   $181.60  
  Purchase #4 $198.95   3.242%   $205.4   $205.40   $205.40   $205.40  
  Purchase #5 $103.81   10.142%   $114.3384   $114.34   $114.35   $114.30  
  Purchase #6 $122.78   3.706%   $127.3302   $127.33   $127.35   $127.30  
  Purchase #7 $114.69   9.569%   $125.6647   $125.66   $125.65   $125.70  
  7 purchase totals = $992.27       $1,084.0403   $1,084.04   $1,084.10   $1,084.00