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 $26.31   3.335%   $27.1874   $27.19   $27.20   $27.20  
  Purchase #2 $176.76   7.296%   $189.6564   $189.66   $189.65   $189.70  
  Purchase #3 $164.99   7.612%   $177.549   $177.55   $177.55   $177.50  
  Purchase #4 $207.85   5.682%   $219.66   $219.66   $219.65   $219.70  
  Purchase #5 $175.70   11.438%   $195.7966   $195.80   $195.80   $195.80  
  Purchase #6 $200.75   12.683%   $226.2111   $226.21   $226.20   $226.20  
  Purchase #7 $184.25   11.787%   $205.9675   $205.97   $205.95   $206.00  
  7 purchase totals = $1,136.61       $1,242.0280   $1,242.04   $1,242.00   $1,242.10