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 $8.90   7.624%   $9.5785   $9.58   $9.60   $9.60  
  Purchase #2 $186.57   9.439%   $204.1803   $204.18   $204.20   $204.20  
  Purchase #3 $113.76   5.184%   $119.6573   $119.66   $119.65   $119.70  
  Purchase #4 $79.69   9.834%   $87.5267   $87.53   $87.55   $87.50  
  Purchase #5 $43.46   7.561%   $46.746   $46.75   $46.75   $46.70  
  Purchase #6 $227.80   11.608%   $254.243   $254.24   $254.25   $254.20  
  Purchase #7 $39.88   3.647%   $41.3344   $41.33   $41.35   $41.30  
  7 purchase totals = $700.06       $763.2662   $763.27   $763.35   $763.20