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 $246.70   8.239%   $267.0256   $267.03   $267.05   $267.00  
  Purchase #2 $141.52   4.580%   $148.0016   $148.00   $148.00   $148.00  
  Purchase #3 $177.69   11.548%   $198.2096   $198.21   $198.20   $198.20  
  Purchase #4 $105.58   9.830%   $115.9585   $115.96   $115.95   $116.00  
  Purchase #5 $58.39   3.611%   $60.4985   $60.50   $60.50   $60.50  
  Purchase #6 $112.45   7.796%   $121.2166   $121.22   $121.20   $121.20  
  Purchase #7 $234.60   13.712%   $266.7684   $266.77   $266.75   $266.80  
  7 purchase totals = $1,076.93       $1,177.6788   $1,177.69   $1,177.65   $1,177.70