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 $88.54   11.243%   $98.4946   $98.49   $98.50   $98.50  
  Purchase #2 $12.77   3.766%   $13.2509   $13.25   $13.25   $13.30  
  Purchase #3 $156.75   3.476%   $162.1986   $162.20   $162.20   $162.20  
  Purchase #4 $52.94   6.847%   $56.5648   $56.56   $56.55   $56.60  
  Purchase #5 $175.75   8.163%   $190.0965   $190.10   $190.10   $190.10  
  Purchase #6 $106.52   10.736%   $117.956   $117.96   $117.95   $118.00  
  Purchase #7 $214.85   6.477%   $228.7658   $228.77   $228.75   $228.80  
  7 purchase totals = $808.12       $867.3272   $867.33   $867.30   $867.50