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 $26.94   10.159%   $29.6768   $29.68   $29.70   $29.70  
  Purchase #2 $136.65   10.416%   $150.8835   $150.88   $150.90   $150.90  
  Purchase #3 $62.38   10.341%   $68.8307   $68.83   $68.85   $68.80  
  Purchase #4 $238.76   5.626%   $252.1926   $252.19   $252.20   $252.20  
  Purchase #5 $176.80   5.741%   $186.9501   $186.95   $186.95   $187.00  
  Purchase #6 $217.90   13.229%   $246.726   $246.73   $246.75   $246.70  
  Purchase #7 $110.64   8.147%   $119.6538   $119.65   $119.65   $119.70  
  7 purchase totals = $970.07       $1,054.9135   $1,054.91   $1,055.00   $1,055.00