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 $59.59   5.674%   $62.9711   $62.97   $62.95   $63.00  
  Purchase #2 $142.92   8.493%   $155.0582   $155.06   $155.05   $155.10  
  Purchase #3 $39.27   3.691%   $40.7195   $40.72   $40.70   $40.70  
  Purchase #4 $243.61   5.306%   $256.5359   $256.54   $256.55   $256.50  
  Purchase #5 $10.74   7.815%   $11.5793   $11.58   $11.60   $11.60  
  Purchase #6 $154.61   6.853%   $165.2054   $165.21   $165.20   $165.20  
  Purchase #7 $203.76   12.835%   $229.9126   $229.91   $229.90   $229.90  
  7 purchase totals = $854.50       $921.9820   $921.99   $921.95   $922.00