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 $63.54   5.491%   $67.029   $67.03   $67.05   $67.00  
  Purchase #2 $203.54   7.775%   $219.3652   $219.37   $219.35   $219.40  
  Purchase #3 $185.99   3.633%   $192.747   $192.75   $192.75   $192.70  
  Purchase #4 $145.26   7.567%   $156.2518   $156.25   $156.25   $156.30  
  Purchase #5 $69.80   9.211%   $76.2293   $76.23   $76.25   $76.20  
  Purchase #6 $217.61   8.114%   $235.2669   $235.27   $235.25   $235.30  
  Purchase #7 $75.83   6.707%   $80.9159   $80.92   $80.90   $80.90  
  7 purchase totals = $961.57       $1,027.8051   $1,027.82   $1,027.80   $1,027.80