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 $47.26   10.599%   $52.2691   $52.27   $52.25   $52.30  
  Purchase #2 $186.74   8.617%   $202.8314   $202.83   $202.85   $202.80  
  Purchase #3 $218.48   6.404%   $232.4715   $232.47   $232.45   $232.50  
  Purchase #4 $77.86   10.823%   $86.2868   $86.29   $86.30   $86.30  
  Purchase #5 $93.38   5.104%   $98.1461   $98.15   $98.15   $98.10  
  Purchase #6 $181.86   9.643%   $199.3968   $199.40   $199.40   $199.40  
  Purchase #7 $110.53   11.474%   $123.2122   $123.21   $123.20   $123.20  
  7 purchase totals = $916.11       $994.6139   $994.62   $994.60   $994.60