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 $173.93   10.746%   $192.6205   $192.62   $192.60   $192.60  
  Purchase #2 $183.47   9.289%   $200.5125   $200.51   $200.50   $200.50  
  Purchase #3 $163.86   6.290%   $174.1668   $174.17   $174.15   $174.20  
  Purchase #4 $247.58   10.602%   $273.8284   $273.83   $273.85   $273.80  
  Purchase #5 $19.72   11.157%   $21.9202   $21.92   $21.90   $21.90  
  Purchase #6 $132.96   8.763%   $144.6113   $144.61   $144.60   $144.60  
  Purchase #7 $243.74   10.290%   $268.8208   $268.82   $268.80   $268.80  
  7 purchase totals = $1,165.26       $1,276.4805   $1,276.48   $1,276.40   $1,276.40