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 $61.40   13.403%   $69.6294   $69.63   $69.65   $69.60  
  Purchase #2 $22.55   4.123%   $23.4797   $23.48   $23.50   $23.50  
  Purchase #3 $235.55   13.540%   $267.4435   $267.44   $267.45   $267.40  
  Purchase #4 $240.85   12.283%   $270.4336   $270.43   $270.45   $270.40  
  Purchase #5 $128.44   10.268%   $141.6282   $141.63   $141.65   $141.60  
  Purchase #6 $11.58   7.327%   $12.4285   $12.43   $12.45   $12.40  
  Purchase #7 $178.39   3.131%   $183.9754   $183.98   $184.00   $184.00  
  7 purchase totals = $878.76       $969.0183   $969.02   $969.15   $968.90