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 $246.65   7.833%   $265.9701   $265.97   $265.95   $266.00  
  Purchase #2 $176.46   9.139%   $192.5867   $192.59   $192.60   $192.60  
  Purchase #3 $66.36   5.565%   $70.0529   $70.05   $70.05   $70.10  
  Purchase #4 $202.86   8.227%   $219.5493   $219.55   $219.55   $219.50  
  Purchase #5 $160.71   12.669%   $181.0703   $181.07   $181.05   $181.10  
  Purchase #6 $147.76   8.618%   $160.494   $160.49   $160.50   $160.50  
  Purchase #7 $166.30   3.511%   $172.1388   $172.14   $172.15   $172.10  
  7 purchase totals = $1,167.10       $1,261.8621   $1,261.86   $1,261.85   $1,261.90