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 $195.74   6.518%   $208.4983   $208.50   $208.50   $208.50  
  Purchase #2 $52.37   8.772%   $56.9639   $56.96   $56.95   $57.00  
  Purchase #3 $229.83   7.591%   $247.2764   $247.28   $247.30   $247.30  
  Purchase #4 $109.88   12.241%   $123.3304   $123.33   $123.35   $123.30  
  Purchase #5 $232.48   11.764%   $259.8289   $259.83   $259.85   $259.80  
  Purchase #6 $177.78   8.494%   $192.8806   $192.88   $192.90   $192.90  
  Purchase #7 $61.80   11.588%   $68.9614   $68.96   $68.95   $69.00  
  7 purchase totals = $1,059.88       $1,157.7399   $1,157.74   $1,157.80   $1,157.80