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 $55.39   10.215%   $61.0481   $61.05   $61.05   $61.00  
  Purchase #2 $204.90   5.760%   $216.7022   $216.70   $216.70   $216.70  
  Purchase #3 $57.97   6.543%   $61.763   $61.76   $61.75   $61.80  
  Purchase #4 $23.28   10.285%   $25.6743   $25.67   $25.65   $25.70  
  Purchase #5 $8.27   11.826%   $9.248   $9.25   $9.25   $9.20  
  Purchase #6 $36.90   4.196%   $38.4483   $38.45   $38.45   $38.40  
  Purchase #7 $157.30   7.107%   $168.4793   $168.48   $168.50   $168.50  
  7 purchase totals = $544.01       $581.3632   $581.36   $581.35   $581.30