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 $241.60   9.538%   $264.6438   $264.64   $264.65   $264.60  
  Purchase #2 $30.65   6.608%   $32.6754   $32.68   $32.70   $32.70  
  Purchase #3 $86.76   13.331%   $98.326   $98.33   $98.35   $98.30  
  Purchase #4 $104.78   5.270%   $110.3019   $110.30   $110.30   $110.30  
  Purchase #5 $76.65   5.299%   $80.7117   $80.71   $80.70   $80.70  
  Purchase #6 $224.79   3.768%   $233.2601   $233.26   $233.25   $233.30  
  Purchase #7 $173.72   11.184%   $193.1488   $193.15   $193.15   $193.10  
  7 purchase totals = $938.95       $1,013.0677   $1,013.07   $1,013.10   $1,013.00