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 $59.89   13.471%   $67.9578   $67.96   $67.95   $68.00  
  Purchase #2 $19.69   11.567%   $21.9675   $21.97   $21.95   $22.00  
  Purchase #3 $156.29   11.482%   $174.2352   $174.24   $174.25   $174.20  
  Purchase #4 $29.29   5.452%   $30.8869   $30.89   $30.90   $30.90  
  Purchase #5 $183.30   13.401%   $207.864   $207.86   $207.85   $207.90  
  Purchase #6 $124.61   12.772%   $140.5252   $140.53   $140.55   $140.50  
  Purchase #7 $211.25   5.279%   $222.4019   $222.40   $222.40   $222.40  
  7 purchase totals = $784.32       $865.8385   $865.85   $865.85   $865.90