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 $33.26   5.321%   $35.0298   $35.03   $35.05   $35.00  
  Purchase #2 $5.54   6.756%   $5.9143   $5.91   $5.90   $5.90  
  Purchase #3 $62.68   13.744%   $71.2947   $71.29   $71.30   $71.30  
  Purchase #4 $77.39   13.117%   $87.5412   $87.54   $87.55   $87.50  
  Purchase #5 $166.93   7.129%   $178.8304   $178.83   $178.85   $178.80  
  Purchase #6 $245.81   6.646%   $262.1465   $262.15   $262.15   $262.10  
  Purchase #7 $177.68   8.423%   $192.646   $192.65   $192.65   $192.60  
  7 purchase totals = $769.29       $833.4029   $833.40   $833.45   $833.20