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 $242.35   8.528%   $263.0176   $263.02   $263.00   $263.00  
  Purchase #2 $84.69   10.574%   $93.6451   $93.65   $93.65   $93.60  
  Purchase #3 $222.46   3.585%   $230.4352   $230.44   $230.45   $230.40  
  Purchase #4 $152.60   8.477%   $165.5359   $165.54   $165.55   $165.50  
  Purchase #5 $21.95   10.201%   $24.1891   $24.19   $24.20   $24.20  
  Purchase #6 $167.37   11.646%   $186.8619   $186.86   $186.85   $186.90  
  Purchase #7 $249.55   6.829%   $266.5918   $266.59   $266.60   $266.60  
  7 purchase totals = $1,140.97       $1,230.2766   $1,230.29   $1,230.30   $1,230.20