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 $226.49   11.307%   $252.0992   $252.10   $252.10   $252.10  
  Purchase #2 $190.44   10.601%   $210.6285   $210.63   $210.65   $210.60  
  Purchase #3 $38.60   13.718%   $43.8951   $43.90   $43.90   $43.90  
  Purchase #4 $112.66   5.404%   $118.7481   $118.75   $118.75   $118.70  
  Purchase #5 $186.52   6.213%   $198.1085   $198.11   $198.10   $198.10  
  Purchase #6 $189.57   9.731%   $208.0171   $208.02   $208.00   $208.00  
  Purchase #7 $203.66   5.739%   $215.348   $215.35   $215.35   $215.30  
  7 purchase totals = $1,147.94       $1,246.8445   $1,246.86   $1,246.85   $1,246.70