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 $56.32   13.547%   $63.9497   $63.95   $63.95   $63.90  
  Purchase #2 $200.56   3.548%   $207.6759   $207.68   $207.70   $207.70  
  Purchase #3 $117.71   12.646%   $132.5956   $132.60   $132.60   $132.60  
  Purchase #4 $87.41   10.729%   $96.7882   $96.79   $96.80   $96.80  
  Purchase #5 $85.58   11.294%   $95.2454   $95.25   $95.25   $95.20  
  Purchase #6 $19.45   13.168%   $22.0112   $22.01   $22.00   $22.00  
  Purchase #7 $103.78   9.387%   $113.5218   $113.52   $113.50   $113.50  
  7 purchase totals = $670.81       $731.7878   $731.80   $731.80   $731.70