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 $137.60   12.161%   $154.3335   $154.33   $154.35   $154.30  
  Purchase #2 $45.84   10.234%   $50.5313   $50.53   $50.55   $50.50  
  Purchase #3 $84.38   13.799%   $96.0236   $96.02   $96.00   $96.00  
  Purchase #4 $40.35   9.835%   $44.3184   $44.32   $44.30   $44.30  
  Purchase #5 $245.27   8.112%   $265.1663   $265.17   $265.15   $265.20  
  Purchase #6 $201.89   11.368%   $224.8409   $224.84   $224.85   $224.80  
  Purchase #7 $35.30   13.465%   $40.0531   $40.05   $40.05   $40.10  
  7 purchase totals = $790.63       $875.2671   $875.26   $875.25   $875.20