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 $11.58   3.743%   $12.0134   $12.01   $12.00   $12.00  
  Purchase #2 $166.27   5.481%   $175.3833   $175.38   $175.40   $175.40  
  Purchase #3 $151.39   11.398%   $168.6454   $168.65   $168.65   $168.60  
  Purchase #4 $54.64   4.740%   $57.2299   $57.23   $57.25   $57.20  
  Purchase #5 $217.78   11.287%   $242.3608   $242.36   $242.35   $242.40  
  Purchase #6 $214.47   9.836%   $235.5653   $235.57   $235.55   $235.60  
  Purchase #7 $54.93   10.688%   $60.8009   $60.80   $60.80   $60.80  
  7 purchase totals = $871.06       $951.9990   $952.00   $952.00   $952.00