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 $127.76   6.464%   $136.0184   $136.02   $136.00   $136.00  
  Purchase #2 $242.59   4.514%   $253.5405   $253.54   $253.55   $253.50  
  Purchase #3 $151.70   3.340%   $156.7668   $156.77   $156.75   $156.80  
  Purchase #4 $55.83   13.779%   $63.5228   $63.52   $63.50   $63.50  
  Purchase #5 $121.72   9.777%   $133.6206   $133.62   $133.60   $133.60  
  Purchase #6 $232.29   11.576%   $259.1799   $259.18   $259.20   $259.20  
  Purchase #7 $163.57   3.220%   $168.837   $168.84   $168.85   $168.80  
  7 purchase totals = $1,095.46       $1,171.4860   $1,171.49   $1,171.45   $1,171.40