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 $51.41   10.494%   $56.805   $56.81   $56.80   $56.80  
  Purchase #2 $219.55   3.497%   $227.2277   $227.23   $227.25   $227.20  
  Purchase #3 $64.34   6.307%   $68.3979   $68.40   $68.40   $68.40  
  Purchase #4 $177.74   6.774%   $189.7801   $189.78   $189.80   $189.80  
  Purchase #5 $78.48   6.652%   $83.7005   $83.70   $83.70   $83.70  
  Purchase #6 $114.94   4.872%   $120.5399   $120.54   $120.55   $120.50  
  Purchase #7 $62.27   11.695%   $69.5525   $69.55   $69.55   $69.60  
  7 purchase totals = $768.73       $816.0036   $816.01   $816.05   $816.00