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 $206.81   9.739%   $226.9512   $226.95   $226.95   $227.00  
  Purchase #2 $20.44   12.575%   $23.0103   $23.01   $23.00   $23.00  
  Purchase #3 $54.66   8.865%   $59.5056   $59.51   $59.50   $59.50  
  Purchase #4 $148.38   6.166%   $157.5291   $157.53   $157.55   $157.50  
  Purchase #5 $45.34   8.728%   $49.2973   $49.30   $49.30   $49.30  
  Purchase #6 $178.30   9.822%   $195.8126   $195.81   $195.80   $195.80  
  Purchase #7 $60.62   11.668%   $67.6931   $67.69   $67.70   $67.70  
  7 purchase totals = $714.55       $779.7992   $779.80   $779.80   $779.80