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 $134.64   12.115%   $150.9516   $150.95   $150.95   $151.00  
  Purchase #2 $185.42   5.149%   $194.9673   $194.97   $194.95   $195.00  
  Purchase #3 $247.75   3.171%   $255.6062   $255.61   $255.60   $255.60  
  Purchase #4 $55.85   13.604%   $63.4478   $63.45   $63.45   $63.40  
  Purchase #5 $66.35   9.487%   $72.6446   $72.64   $72.65   $72.60  
  Purchase #6 $173.29   11.870%   $193.8595   $193.86   $193.85   $193.90  
  Purchase #7 $109.28   13.563%   $124.1016   $124.10   $124.10   $124.10  
  7 purchase totals = $972.58       $1,055.5786   $1,055.58   $1,055.55   $1,055.60