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 $178.58   4.486%   $186.5911   $186.59   $186.60   $186.60  
  Purchase #2 $35.86   9.654%   $39.3219   $39.32   $39.30   $39.30  
  Purchase #3 $41.75   5.392%   $44.0012   $44.00   $44.00   $44.00  
  Purchase #4 $218.88   6.308%   $232.687   $232.69   $232.70   $232.70  
  Purchase #5 $140.63   13.707%   $159.9062   $159.91   $159.90   $159.90  
  Purchase #6 $100.64   3.616%   $104.2791   $104.28   $104.30   $104.30  
  Purchase #7 $229.69   10.805%   $254.508   $254.51   $254.50   $254.50  
  7 purchase totals = $946.03       $1,021.2945   $1,021.30   $1,021.30   $1,021.30