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 $180.63   9.482%   $197.7573   $197.76   $197.75   $197.80  
  Purchase #2 $132.26   11.534%   $147.5149   $147.51   $147.50   $147.50  
  Purchase #3 $34.63   7.619%   $37.2685   $37.27   $37.25   $37.30  
  Purchase #4 $175.79   9.528%   $192.5393   $192.54   $192.55   $192.50  
  Purchase #5 $42.72   9.485%   $46.772   $46.77   $46.75   $46.80  
  Purchase #6 $212.87   6.605%   $226.9301   $226.93   $226.95   $226.90  
  Purchase #7 $143.93   11.740%   $160.8274   $160.83   $160.85   $160.80  
  7 purchase totals = $922.83       $1,009.6095   $1,009.61   $1,009.60   $1,009.60