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 $243.76   8.233%   $263.8288   $263.83   $263.85   $263.80  
  Purchase #2 $132.85   11.145%   $147.6561   $147.66   $147.65   $147.70  
  Purchase #3 $53.46   10.395%   $59.0172   $59.02   $59.00   $59.00  
  Purchase #4 $212.29   13.856%   $241.7049   $241.70   $241.70   $241.70  
  Purchase #5 $122.61   6.852%   $131.0112   $131.01   $131.00   $131.00  
  Purchase #6 $162.47   5.457%   $171.336   $171.34   $171.35   $171.30  
  Purchase #7 $58.80   8.577%   $63.8433   $63.84   $63.85   $63.80  
  7 purchase totals = $986.24       $1,078.3975   $1,078.40   $1,078.40   $1,078.30