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 $77.65   6.385%   $82.608   $82.61   $82.60   $82.60  
  Purchase #2 $39.26   11.305%   $43.6983   $43.70   $43.70   $43.70  
  Purchase #3 $77.83   12.495%   $87.5549   $87.55   $87.55   $87.60  
  Purchase #4 $47.58   6.757%   $50.795   $50.80   $50.80   $50.80  
  Purchase #5 $145.87   7.765%   $157.1968   $157.20   $157.20   $157.20  
  Purchase #6 $73.91   13.574%   $83.9425   $83.94   $83.95   $83.90  
  Purchase #7 $167.74   11.315%   $186.7198   $186.72   $186.70   $186.70  
  7 purchase totals = $629.84       $692.5153   $692.52   $692.50   $692.50