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 $166.86   10.636%   $184.6072   $184.61   $184.60   $184.60  
  Purchase #2 $199.93   11.167%   $222.2562   $222.26   $222.25   $222.30  
  Purchase #3 $230.46   8.615%   $250.3141   $250.31   $250.30   $250.30  
  Purchase #4 $17.29   6.407%   $18.3978   $18.40   $18.40   $18.40  
  Purchase #5 $177.97   6.460%   $189.4669   $189.47   $189.45   $189.50  
  Purchase #6 $86.88   8.515%   $94.2778   $94.28   $94.30   $94.30  
  Purchase #7 $106.38   8.496%   $115.418   $115.42   $115.40   $115.40  
  7 purchase totals = $985.77       $1,074.7380   $1,074.75   $1,074.70   $1,074.80