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 $208.28   11.367%   $231.9552   $231.96   $231.95   $232.00  
  Purchase #2 $135.37   9.445%   $148.1557   $148.16   $148.15   $148.20  
  Purchase #3 $137.33   4.411%   $143.3876   $143.39   $143.40   $143.40  
  Purchase #4 $142.40   13.196%   $161.1911   $161.19   $161.20   $161.20  
  Purchase #5 $243.41   7.850%   $262.5177   $262.52   $262.50   $262.50  
  Purchase #6 $44.41   11.397%   $49.4714   $49.47   $49.45   $49.50  
  Purchase #7 $25.63   5.697%   $27.0901   $27.09   $27.10   $27.10  
  7 purchase totals = $936.83       $1,023.7688   $1,023.78   $1,023.75   $1,023.90