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 $209.96   4.124%   $218.6188   $218.62   $218.60   $218.60  
  Purchase #2 $63.86   5.470%   $67.3531   $67.35   $67.35   $67.40  
  Purchase #3 $214.46   10.370%   $236.6995   $236.70   $236.70   $236.70  
  Purchase #4 $111.77   8.687%   $121.4795   $121.48   $121.50   $121.50  
  Purchase #5 $49.25   8.738%   $53.5535   $53.55   $53.55   $53.60  
  Purchase #6 $229.74   10.335%   $253.4836   $253.48   $253.50   $253.50  
  Purchase #7 $37.33   11.620%   $41.6677   $41.67   $41.65   $41.70  
  7 purchase totals = $916.37       $992.8557   $992.85   $992.85   $993.00