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 $245.73   10.483%   $271.4899   $271.49   $271.50   $271.50  
  Purchase #2 $167.59   5.277%   $176.4337   $176.43   $176.45   $176.40  
  Purchase #3 $26.75   9.406%   $29.2661   $29.27   $29.25   $29.30  
  Purchase #4 $24.73   12.405%   $27.7978   $27.80   $27.80   $27.80  
  Purchase #5 $221.92   3.551%   $229.8004   $229.80   $229.80   $229.80  
  Purchase #6 $83.85   8.144%   $90.6787   $90.68   $90.70   $90.70  
  Purchase #7 $210.95   11.163%   $234.4983   $234.50   $234.50   $234.50  
  7 purchase totals = $981.52       $1,059.9649   $1,059.97   $1,060.00   $1,060.00