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 $174.92   9.808%   $192.0762   $192.08   $192.10   $192.10  
  Purchase #2 $209.64   4.193%   $218.4302   $218.43   $218.45   $218.40  
  Purchase #3 $217.31   11.844%   $243.0482   $243.05   $243.05   $243.00  
  Purchase #4 $200.76   3.271%   $207.3269   $207.33   $207.35   $207.30  
  Purchase #5 $114.93   13.123%   $130.0123   $130.01   $130.00   $130.00  
  Purchase #6 $160.25   12.171%   $179.754   $179.75   $179.75   $179.80  
  Purchase #7 $51.95   8.106%   $56.1611   $56.16   $56.15   $56.20  
  7 purchase totals = $1,129.76       $1,226.8089   $1,226.81   $1,226.85   $1,226.80