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 $227.58   9.550%   $249.3139   $249.31   $249.30   $249.30  
  Purchase #2 $220.33   3.834%   $228.7775   $228.78   $228.80   $228.80  
  Purchase #3 $33.33   10.183%   $36.724   $36.72   $36.70   $36.70  
  Purchase #4 $125.45   6.566%   $133.687   $133.69   $133.70   $133.70  
  Purchase #5 $76.69   12.153%   $86.0101   $86.01   $86.00   $86.00  
  Purchase #6 $43.64   7.246%   $46.8022   $46.80   $46.80   $46.80  
  Purchase #7 $243.64   3.232%   $251.5144   $251.51   $251.50   $251.50  
  7 purchase totals = $970.66       $1,032.8291   $1,032.82   $1,032.80   $1,032.80