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 $141.26   7.603%   $152   $152.00   $152.00   $152.00  
  Purchase #2 $81.85   11.412%   $91.1907   $91.19   $91.20   $91.20  
  Purchase #3 $221.50   6.188%   $235.2064   $235.21   $235.20   $235.20  
  Purchase #4 $76.83   6.617%   $81.9138   $81.91   $81.90   $81.90  
  Purchase #5 $46.26   3.346%   $47.8079   $47.81   $47.80   $47.80  
  Purchase #6 $228.90   12.116%   $256.6335   $256.63   $256.65   $256.60  
  Purchase #7 $45.91   9.481%   $50.2627   $50.26   $50.25   $50.30  
  7 purchase totals = $842.51       $915.0150   $915.01   $915.00   $915.00