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 $52.99   6.162%   $56.2552   $56.26   $56.25   $56.30  
  Purchase #2 $224.58   3.725%   $232.9456   $232.95   $232.95   $232.90  
  Purchase #3 $190.72   10.741%   $211.2052   $211.21   $211.20   $211.20  
  Purchase #4 $35.45   7.198%   $38.0017   $38.00   $38.00   $38.00  
  Purchase #5 $186.95   8.528%   $202.8931   $202.89   $202.90   $202.90  
  Purchase #6 $238.94   12.485%   $268.7717   $268.77   $268.75   $268.80  
  Purchase #7 $32.63   11.822%   $36.4875   $36.49   $36.50   $36.50  
  7 purchase totals = $962.26       $1,046.5600   $1,046.57   $1,046.55   $1,046.60