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 $58.62   12.142%   $65.7376   $65.74   $65.75   $65.70  
  Purchase #2 $111.37   6.518%   $118.6291   $118.63   $118.65   $118.60  
  Purchase #3 $82.28   11.549%   $91.7825   $91.78   $91.80   $91.80  
  Purchase #4 $13.57   8.771%   $14.7602   $14.76   $14.75   $14.80  
  Purchase #5 $99.41   6.286%   $105.6589   $105.66   $105.65   $105.70  
  Purchase #6 $95.93   13.628%   $109.0033   $109.00   $109.00   $109.00  
  Purchase #7 $214.91   12.119%   $240.9549   $240.95   $240.95   $241.00  
  7 purchase totals = $676.09       $746.5265   $746.52   $746.55   $746.60