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 $168.95   8.220%   $182.8377   $182.84   $182.85   $182.80  
  Purchase #2 $141.61   9.116%   $154.5192   $154.52   $154.50   $154.50  
  Purchase #3 $179.50   3.874%   $186.4538   $186.45   $186.45   $186.50  
  Purchase #4 $95.49   11.513%   $106.4838   $106.48   $106.50   $106.50  
  Purchase #5 $60.94   8.139%   $65.8999   $65.90   $65.90   $65.90  
  Purchase #6 $241.40   12.173%   $270.7856   $270.79   $270.80   $270.80  
  Purchase #7 $29.75   11.790%   $33.2575   $33.26   $33.25   $33.30  
  7 purchase totals = $917.64       $1,000.2375   $1,000.24   $1,000.25   $1,000.30