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 $241.52   8.693%   $262.5153   $262.52   $262.50   $262.50  
  Purchase #2 $126.78   12.786%   $142.9901   $142.99   $143.00   $143.00  
  Purchase #3 $130.95   11.679%   $146.2437   $146.24   $146.25   $146.20  
  Purchase #4 $224.94   3.454%   $232.7094   $232.71   $232.70   $232.70  
  Purchase #5 $229.71   7.549%   $247.0508   $247.05   $247.05   $247.10  
  Purchase #6 $236.26   6.593%   $251.8366   $251.84   $251.85   $251.80  
  Purchase #7 $118.35   10.355%   $130.6051   $130.61   $130.60   $130.60  
  7 purchase totals = $1,308.51       $1,413.9510   $1,413.96   $1,413.95   $1,413.90