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 $214.54   9.772%   $235.5048   $235.50   $235.50   $235.50  
  Purchase #2 $114.31   11.742%   $127.7323   $127.73   $127.75   $127.70  
  Purchase #3 $117.41   12.153%   $131.6788   $131.68   $131.70   $131.70  
  Purchase #4 $119.95   7.639%   $129.113   $129.11   $129.10   $129.10  
  Purchase #5 $193.95   6.444%   $206.4481   $206.45   $206.45   $206.40  
  Purchase #6 $70.42   6.288%   $74.848   $74.85   $74.85   $74.80  
  Purchase #7 $52.70   6.867%   $56.3189   $56.32   $56.30   $56.30  
  7 purchase totals = $883.28       $961.6439   $961.64   $961.65   $961.50