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 $203.81   10.167%   $224.5314   $224.53   $224.55   $224.50  
  Purchase #2 $95.28   12.189%   $106.8937   $106.89   $106.90   $106.90  
  Purchase #3 $98.70   13.315%   $111.8419   $111.84   $111.85   $111.80  
  Purchase #4 $58.53   3.646%   $60.664   $60.66   $60.65   $60.70  
  Purchase #5 $150.53   10.477%   $166.301   $166.30   $166.30   $166.30  
  Purchase #6 $122.67   7.265%   $131.582   $131.58   $131.60   $131.60  
  Purchase #7 $237.68   6.146%   $252.2878   $252.29   $252.30   $252.30  
  7 purchase totals = $967.20       $1,054.1018   $1,054.09   $1,054.15   $1,054.10