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 $240.76   11.840%   $269.266   $269.27   $269.25   $269.30  
  Purchase #2 $24.28   9.595%   $26.6097   $26.61   $26.60   $26.60  
  Purchase #3 $139.59   8.842%   $151.9325   $151.93   $151.95   $151.90  
  Purchase #4 $210.87   5.134%   $221.6961   $221.70   $221.70   $221.70  
  Purchase #5 $206.90   9.176%   $225.8851   $225.89   $225.90   $225.90  
  Purchase #6 $118.62   7.273%   $127.2472   $127.25   $127.25   $127.20  
  Purchase #7 $121.47   6.665%   $129.566   $129.57   $129.55   $129.60  
  7 purchase totals = $1,062.49       $1,152.2026   $1,152.22   $1,152.20   $1,152.20