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 $61.63   13.262%   $69.8034   $69.80   $69.80   $69.80  
  Purchase #2 $221.47   8.799%   $240.9571   $240.96   $240.95   $241.00  
  Purchase #3 $88.76   5.306%   $93.4696   $93.47   $93.45   $93.50  
  Purchase #4 $77.80   9.364%   $85.0852   $85.09   $85.10   $85.10  
  Purchase #5 $119.80   5.509%   $126.3998   $126.40   $126.40   $126.40  
  Purchase #6 $144.65   5.791%   $153.0267   $153.03   $153.05   $153.00  
  Purchase #7 $53.32   9.581%   $58.4286   $58.43   $58.45   $58.40  
  7 purchase totals = $767.43       $827.1704   $827.18   $827.20   $827.20