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 $56.91   11.772%   $63.6094   $63.61   $63.60   $63.60  
  Purchase #2 $172.28   7.352%   $184.946   $184.95   $184.95   $184.90  
  Purchase #3 $11.94   7.153%   $12.7941   $12.79   $12.80   $12.80  
  Purchase #4 $204.50   8.523%   $221.9295   $221.93   $221.95   $221.90  
  Purchase #5 $27.95   5.316%   $29.4358   $29.44   $29.45   $29.40  
  Purchase #6 $189.76   11.159%   $210.9353   $210.94   $210.95   $210.90  
  Purchase #7 $177.30   9.250%   $193.7003   $193.70   $193.70   $193.70  
  7 purchase totals = $840.64       $917.3504   $917.36   $917.40   $917.20