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 $143.69   10.860%   $159.2947   $159.29   $159.30   $159.30  
  Purchase #2 $90.47   10.189%   $99.688   $99.69   $99.70   $99.70  
  Purchase #3 $72.52   13.513%   $82.3196   $82.32   $82.30   $82.30  
  Purchase #4 $226.66   11.189%   $252.021   $252.02   $252.00   $252.00  
  Purchase #5 $159.31   12.230%   $178.7936   $178.79   $178.80   $178.80  
  Purchase #6 $175.53   9.517%   $192.2352   $192.24   $192.25   $192.20  
  Purchase #7 $46.34   7.793%   $49.9513   $49.95   $49.95   $50.00  
  7 purchase totals = $914.52       $1,014.3034   $1,014.30   $1,014.30   $1,014.30