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 $103.32   12.496%   $116.2309   $116.23   $116.25   $116.20  
  Purchase #2 $235.92   11.367%   $262.737   $262.74   $262.75   $262.70  
  Purchase #3 $54.27   13.450%   $61.5693   $61.57   $61.55   $61.60  
  Purchase #4 $227.60   12.116%   $255.176   $255.18   $255.20   $255.20  
  Purchase #5 $161.98   3.806%   $168.145   $168.15   $168.15   $168.10  
  Purchase #6 $115.60   5.125%   $121.5245   $121.52   $121.50   $121.50  
  Purchase #7 $88.61   8.318%   $95.9806   $95.98   $96.00   $96.00  
  7 purchase totals = $987.30       $1,081.3633   $1,081.37   $1,081.40   $1,081.30