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 $69.52   8.686%   $75.5585   $75.56   $75.55   $75.60  
  Purchase #2 $66.26   12.856%   $74.7784   $74.78   $74.80   $74.80  
  Purchase #3 $61.62   8.863%   $67.0814   $67.08   $67.10   $67.10  
  Purchase #4 $192.77   5.475%   $203.3242   $203.32   $203.30   $203.30  
  Purchase #5 $205.91   5.819%   $217.8919   $217.89   $217.90   $217.90  
  Purchase #6 $131.25   3.809%   $136.2493   $136.25   $136.25   $136.20  
  Purchase #7 $247.54   8.807%   $269.3408   $269.34   $269.35   $269.30  
  7 purchase totals = $974.87       $1,044.2245   $1,044.22   $1,044.25   $1,044.20