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 $86.34   11.670%   $96.4159   $96.42   $96.40   $96.40  
  Purchase #2 $184.93   3.359%   $191.1418   $191.14   $191.15   $191.10  
  Purchase #3 $146.58   4.563%   $153.2684   $153.27   $153.25   $153.30  
  Purchase #4 $233.90   12.696%   $263.5959   $263.60   $263.60   $263.60  
  Purchase #5 $162.74   12.432%   $182.9718   $182.97   $182.95   $183.00  
  Purchase #6 $24.55   5.199%   $25.8264   $25.83   $25.85   $25.80  
  Purchase #7 $127.51   6.464%   $135.7522   $135.75   $135.75   $135.80  
  7 purchase totals = $966.55       $1,048.9724   $1,048.98   $1,048.95   $1,049.00