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 $232.47   13.524%   $263.9092   $263.91   $263.90   $263.90  
  Purchase #2 $218.84   13.645%   $248.7007   $248.70   $248.70   $248.70  
  Purchase #3 $55.39   6.856%   $59.1875   $59.19   $59.20   $59.20  
  Purchase #4 $131.33   5.442%   $138.477   $138.48   $138.50   $138.50  
  Purchase #5 $156.40   10.557%   $172.9111   $172.91   $172.90   $172.90  
  Purchase #6 $73.70   5.262%   $77.5781   $77.58   $77.60   $77.60  
  Purchase #7 $61.93   11.451%   $69.0216   $69.02   $69.00   $69.00  
  7 purchase totals = $930.06       $1,029.7852   $1,029.79   $1,029.80   $1,029.80