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 $193.33   5.397%   $203.764   $203.76   $203.75   $203.80  
  Purchase #2 $136.38   8.256%   $147.6395   $147.64   $147.65   $147.60  
  Purchase #3 $181.26   3.644%   $187.8651   $187.87   $187.85   $187.90  
  Purchase #4 $248.87   4.626%   $260.3827   $260.38   $260.40   $260.40  
  Purchase #5 $192.85   12.303%   $216.5763   $216.58   $216.60   $216.60  
  Purchase #6 $49.89   12.704%   $56.228   $56.23   $56.25   $56.20  
  Purchase #7 $203.87   3.248%   $210.4917   $210.49   $210.50   $210.50  
  7 purchase totals = $1,206.45       $1,282.9473   $1,282.95   $1,283.00   $1,283.00