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 $33.59   5.797%   $35.5372   $35.54   $35.55   $35.50  
  Purchase #2 $142.71   3.468%   $147.6592   $147.66   $147.65   $147.70  
  Purchase #3 $70.62   5.800%   $74.716   $74.72   $74.70   $74.70  
  Purchase #4 $182.75   12.390%   $205.3927   $205.39   $205.40   $205.40  
  Purchase #5 $162.49   5.620%   $171.6219   $171.62   $171.60   $171.60  
  Purchase #6 $24.92   5.295%   $26.2395   $26.24   $26.25   $26.20  
  Purchase #7 $40.26   12.164%   $45.1572   $45.16   $45.15   $45.20  
  7 purchase totals = $657.34       $706.3237   $706.33   $706.30   $706.30