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 $67.25   4.136%   $70.0315   $70.03   $70.05   $70.00  
  Purchase #2 $86.92   12.173%   $97.5008   $97.50   $97.50   $97.50  
  Purchase #3 $169.93   12.401%   $191.003   $191.00   $191.00   $191.00  
  Purchase #4 $79.58   4.409%   $83.0887   $83.09   $83.10   $83.10  
  Purchase #5 $234.27   3.667%   $242.8607   $242.86   $242.85   $242.90  
  Purchase #6 $248.48   4.719%   $260.2058   $260.21   $260.20   $260.20  
  Purchase #7 $85.38   3.693%   $88.5331   $88.53   $88.55   $88.50  
  7 purchase totals = $971.81       $1,033.2236   $1,033.22   $1,033.25   $1,033.20