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 $140.81   9.126%   $153.6603   $153.66   $153.65   $153.70  
  Purchase #2 $49.62   6.665%   $52.9272   $52.93   $52.95   $52.90  
  Purchase #3 $98.58   13.181%   $111.5738   $111.57   $111.55   $111.60  
  Purchase #4 $237.33   13.350%   $269.0136   $269.01   $269.00   $269.00  
  Purchase #5 $203.56   8.229%   $220.311   $220.31   $220.30   $220.30  
  Purchase #6 $116.75   5.391%   $123.044   $123.04   $123.05   $123.00  
  Purchase #7 $137.84   11.742%   $154.0252   $154.03   $154.05   $154.00  
  7 purchase totals = $984.49       $1,084.5551   $1,084.55   $1,084.55   $1,084.50