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 $106.59   5.311%   $112.251   $112.25   $112.25   $112.30  
  Purchase #2 $26.81   11.663%   $29.9369   $29.94   $29.95   $29.90  
  Purchase #3 $244.91   11.209%   $272.362   $272.36   $272.35   $272.40  
  Purchase #4 $148.50   12.272%   $166.7239   $166.72   $166.70   $166.70  
  Purchase #5 $222.97   6.386%   $237.2089   $237.21   $237.20   $237.20  
  Purchase #6 $115.65   3.547%   $119.7521   $119.75   $119.75   $119.80  
  Purchase #7 $148.65   11.309%   $165.4608   $165.46   $165.45   $165.50  
  7 purchase totals = $1,014.08       $1,103.6956   $1,103.69   $1,103.65   $1,103.80