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 $47.41   5.736%   $50.1294   $50.13   $50.15   $50.10  
  Purchase #2 $249.78   7.714%   $269.048   $269.05   $269.05   $269.00  
  Purchase #3 $212.90   7.359%   $228.5673   $228.57   $228.55   $228.60  
  Purchase #4 $71.97   3.503%   $74.4911   $74.49   $74.50   $74.50  
  Purchase #5 $11.27   9.141%   $12.3002   $12.30   $12.30   $12.30  
  Purchase #6 $48.32   10.215%   $53.2559   $53.26   $53.25   $53.30  
  Purchase #7 $12.96   8.255%   $14.0298   $14.03   $14.05   $14.00  
  7 purchase totals = $654.61       $701.8217   $701.83   $701.85   $701.80