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 $178.80   13.761%   $203.4047   $203.40   $203.40   $203.40  
  Purchase #2 $184.69   7.492%   $198.527   $198.53   $198.55   $198.50  
  Purchase #3 $41.43   7.562%   $44.5629   $44.56   $44.55   $44.60  
  Purchase #4 $137.35   5.723%   $145.2105   $145.21   $145.20   $145.20  
  Purchase #5 $139.79   5.476%   $147.4449   $147.44   $147.45   $147.40  
  Purchase #6 $239.36   10.797%   $265.2037   $265.20   $265.20   $265.20  
  Purchase #7 $57.63   13.271%   $65.2781   $65.28   $65.30   $65.30  
  7 purchase totals = $979.05       $1,069.6318   $1,069.62   $1,069.65   $1,069.60