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 $64.85   6.751%   $69.228   $69.23   $69.25   $69.20  
  Purchase #2 $62.70   3.607%   $64.9616   $64.96   $64.95   $65.00  
  Purchase #3 $230.51   9.710%   $252.8925   $252.89   $252.90   $252.90  
  Purchase #4 $246.54   8.503%   $267.5033   $267.50   $267.50   $267.50  
  Purchase #5 $54.90   13.423%   $62.2692   $62.27   $62.25   $62.30  
  Purchase #6 $124.44   4.364%   $129.8706   $129.87   $129.85   $129.90  
  Purchase #7 $78.58   12.419%   $88.3389   $88.34   $88.35   $88.30  
  7 purchase totals = $862.52       $935.0641   $935.06   $935.05   $935.10