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 $62.53   6.481%   $66.5826   $66.58   $66.60   $66.60  
  Purchase #2 $33.38   11.834%   $37.3302   $37.33   $37.35   $37.30  
  Purchase #3 $186.40   8.683%   $202.5851   $202.59   $202.60   $202.60  
  Purchase #4 $100.79   11.315%   $112.1944   $112.19   $112.20   $112.20  
  Purchase #5 $95.52   4.213%   $99.5443   $99.54   $99.55   $99.50  
  Purchase #6 $184.38   7.434%   $198.0868   $198.09   $198.10   $198.10  
  Purchase #7 $169.81   8.249%   $183.8176   $183.82   $183.80   $183.80  
  7 purchase totals = $832.81       $900.1410   $900.14   $900.20   $900.10