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 $93.86   3.250%   $96.9105   $96.91   $96.90   $96.90  
  Purchase #2 $250.79   7.489%   $269.5717   $269.57   $269.55   $269.60  
  Purchase #3 $62.81   7.432%   $67.478   $67.48   $67.50   $67.50  
  Purchase #4 $161.87   8.516%   $175.6548   $175.65   $175.65   $175.70  
  Purchase #5 $77.40   8.367%   $83.8761   $83.88   $83.90   $83.90  
  Purchase #6 $137.67   12.483%   $154.8553   $154.86   $154.85   $154.90  
  Purchase #7 $159.50   10.110%   $175.6255   $175.63   $175.65   $175.60  
  7 purchase totals = $943.90       $1,023.9719   $1,023.98   $1,024.00   $1,024.10