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 $32.35   8.336%   $35.0467   $35.05   $35.05   $35.00  
  Purchase #2 $155.30   7.493%   $166.9366   $166.94   $166.95   $166.90  
  Purchase #3 $84.61   11.573%   $94.4019   $94.40   $94.40   $94.40  
  Purchase #4 $242.58   7.852%   $261.6274   $261.63   $261.65   $261.60  
  Purchase #5 $26.58   6.825%   $28.3941   $28.39   $28.40   $28.40  
  Purchase #6 $41.98   7.546%   $45.1478   $45.15   $45.15   $45.10  
  Purchase #7 $189.87   6.301%   $201.8337   $201.83   $201.85   $201.80  
  7 purchase totals = $773.27       $833.3882   $833.39   $833.45   $833.20