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 $68.44   12.464%   $76.9704   $76.97   $76.95   $77.00  
  Purchase #2 $183.43   5.121%   $192.8235   $192.82   $192.80   $192.80  
  Purchase #3 $134.94   7.430%   $144.966   $144.97   $144.95   $145.00  
  Purchase #4 $156.43   7.704%   $168.4814   $168.48   $168.50   $168.50  
  Purchase #5 $202.93   4.521%   $212.1045   $212.10   $212.10   $212.10  
  Purchase #6 $248.92   8.412%   $269.8592   $269.86   $269.85   $269.90  
  Purchase #7 $221.78   6.244%   $235.6279   $235.63   $235.65   $235.60  
  7 purchase totals = $1,216.87       $1,300.8329   $1,300.83   $1,300.80   $1,300.90