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 $221.32   6.599%   $235.9249   $235.92   $235.90   $235.90  
  Purchase #2 $73.82   4.682%   $77.2763   $77.28   $77.30   $77.30  
  Purchase #3 $62.74   12.489%   $70.5756   $70.58   $70.60   $70.60  
  Purchase #4 $69.64   7.635%   $74.957   $74.96   $74.95   $75.00  
  Purchase #5 $54.31   11.418%   $60.5111   $60.51   $60.50   $60.50  
  Purchase #6 $239.41   9.835%   $262.956   $262.96   $262.95   $263.00  
  Purchase #7 $242.77   9.240%   $265.2019   $265.20   $265.20   $265.20  
  7 purchase totals = $964.01       $1,047.4028   $1,047.41   $1,047.40   $1,047.50