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 $61.84   12.108%   $69.3276   $69.33   $69.35   $69.30  
  Purchase #2 $132.95   13.236%   $150.5473   $150.55   $150.55   $150.50  
  Purchase #3 $234.35   10.231%   $258.3263   $258.33   $258.35   $258.30  
  Purchase #4 $44.43   8.857%   $48.3652   $48.37   $48.35   $48.40  
  Purchase #5 $43.42   12.681%   $48.9261   $48.93   $48.95   $48.90  
  Purchase #6 $234.99   6.734%   $250.8142   $250.81   $250.80   $250.80  
  Purchase #7 $146.44   9.161%   $159.8554   $159.86   $159.85   $159.90  
  7 purchase totals = $898.42       $986.1621   $986.18   $986.20   $986.10