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 $247.83   8.569%   $269.0666   $269.07   $269.05   $269.10  
  Purchase #2 $247.33   3.791%   $256.7063   $256.71   $256.70   $256.70  
  Purchase #3 $177.70   7.594%   $191.1945   $191.19   $191.20   $191.20  
  Purchase #4 $46.98   11.259%   $52.2695   $52.27   $52.25   $52.30  
  Purchase #5 $56.28   4.186%   $58.6359   $58.64   $58.65   $58.60  
  Purchase #6 $233.66   13.367%   $264.8933   $264.89   $264.90   $264.90  
  Purchase #7 $78.27   3.156%   $80.7402   $80.74   $80.75   $80.70  
  7 purchase totals = $1,088.05       $1,173.5063   $1,173.51   $1,173.50   $1,173.50