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 $168.93   8.451%   $183.2063   $183.21   $183.20   $183.20  
  Purchase #2 $204.61   12.385%   $229.9509   $229.95   $229.95   $230.00  
  Purchase #3 $78.86   3.711%   $81.7865   $81.79   $81.80   $81.80  
  Purchase #4 $46.92   8.870%   $51.0818   $51.08   $51.10   $51.10  
  Purchase #5 $235.35   13.704%   $267.6024   $267.60   $267.60   $267.60  
  Purchase #6 $17.32   5.446%   $18.2632   $18.26   $18.25   $18.30  
  Purchase #7 $230.70   12.400%   $259.3068   $259.31   $259.30   $259.30  
  7 purchase totals = $982.69       $1,091.1979   $1,091.20   $1,091.20   $1,091.30