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 $54.80   11.225%   $60.9513   $60.95   $60.95   $61.00  
  Purchase #2 $227.39   4.284%   $237.1314   $237.13   $237.15   $237.10  
  Purchase #3 $169.59   9.606%   $185.8808   $185.88   $185.90   $185.90  
  Purchase #4 $33.44   7.244%   $35.8624   $35.86   $35.85   $35.90  
  Purchase #5 $32.62   9.104%   $35.5897   $35.59   $35.60   $35.60  
  Purchase #6 $69.97   5.814%   $74.0381   $74.04   $74.05   $74.00  
  Purchase #7 $38.79   5.354%   $40.8668   $40.87   $40.85   $40.90  
  7 purchase totals = $626.60       $670.3205   $670.32   $670.35   $670.40