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 $32.92   8.238%   $35.6319   $35.63   $35.65   $35.60  
  Purchase #2 $147.99   4.479%   $154.6185   $154.62   $154.60   $154.60  
  Purchase #3 $63.36   7.265%   $67.9631   $67.96   $67.95   $68.00  
  Purchase #4 $214.82   6.471%   $228.721   $228.72   $228.70   $228.70  
  Purchase #5 $137.64   13.814%   $156.6536   $156.65   $156.65   $156.70  
  Purchase #6 $172.69   10.483%   $190.7931   $190.79   $190.80   $190.80  
  Purchase #7 $36.51   4.867%   $38.2869   $38.29   $38.30   $38.30  
  7 purchase totals = $805.93       $872.6681   $872.66   $872.65   $872.70