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 $176.26   5.822%   $186.5219   $186.52   $186.50   $186.50  
  Purchase #2 $76.75   6.273%   $81.5645   $81.56   $81.55   $81.60  
  Purchase #3 $136.76   12.617%   $154.015   $154.02   $154.00   $154.00  
  Purchase #4 $118.62   13.197%   $134.2743   $134.27   $134.25   $134.30  
  Purchase #5 $228.64   11.219%   $254.2911   $254.29   $254.30   $254.30  
  Purchase #6 $76.99   7.722%   $82.9352   $82.94   $82.95   $82.90  
  Purchase #7 $179.35   13.555%   $203.6609   $203.66   $203.65   $203.70  
  7 purchase totals = $993.37       $1,097.2629   $1,097.26   $1,097.20   $1,097.30