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 $163.59   7.629%   $176.0703   $176.07   $176.05   $176.10  
  Purchase #2 $53.55   12.797%   $60.4028   $60.40   $60.40   $60.40  
  Purchase #3 $58.39   3.699%   $60.5498   $60.55   $60.55   $60.50  
  Purchase #4 $128.46   3.565%   $133.0396   $133.04   $133.05   $133.00  
  Purchase #5 $188.27   8.554%   $204.3746   $204.37   $204.35   $204.40  
  Purchase #6 $173.68   4.455%   $181.4174   $181.42   $181.40   $181.40  
  Purchase #7 $225.75   9.324%   $246.7989   $246.80   $246.80   $246.80  
  7 purchase totals = $991.69       $1,062.6534   $1,062.65   $1,062.60   $1,062.60