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 $218.56   4.869%   $229.2017   $229.20   $229.20   $229.20  
  Purchase #2 $130.58   13.693%   $148.4603   $148.46   $148.45   $148.50  
  Purchase #3 $60.52   12.141%   $67.8677   $67.87   $67.85   $67.90  
  Purchase #4 $178.55   12.757%   $201.3276   $201.33   $201.35   $201.30  
  Purchase #5 $229.45   7.605%   $246.8997   $246.90   $246.90   $246.90  
  Purchase #6 $220.70   5.491%   $232.8186   $232.82   $232.80   $232.80  
  Purchase #7 $116.42   12.377%   $130.8293   $130.83   $130.85   $130.80  
  7 purchase totals = $1,154.78       $1,257.4049   $1,257.41   $1,257.40   $1,257.40