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 $89.82   6.779%   $95.9089   $95.91   $95.90   $95.90  
  Purchase #2 $139.37   7.551%   $149.8938   $149.89   $149.90   $149.90  
  Purchase #3 $21.50   6.470%   $22.8911   $22.89   $22.90   $22.90  
  Purchase #4 $218.74   3.729%   $226.8968   $226.90   $226.90   $226.90  
  Purchase #5 $222.47   11.695%   $248.4879   $248.49   $248.50   $248.50  
  Purchase #6 $14.49   10.759%   $16.049   $16.05   $16.05   $16.00  
  Purchase #7 $178.79   7.631%   $192.4335   $192.43   $192.45   $192.40  
  7 purchase totals = $885.18       $952.5610   $952.56   $952.60   $952.50