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 $57.91   4.252%   $60.3723   $60.37   $60.35   $60.40  
  Purchase #2 $24.64   8.448%   $26.7216   $26.72   $26.70   $26.70  
  Purchase #3 $231.43   8.608%   $251.3515   $251.35   $251.35   $251.40  
  Purchase #4 $93.90   11.449%   $104.6506   $104.65   $104.65   $104.70  
  Purchase #5 $242.51   8.155%   $262.2867   $262.29   $262.30   $262.30  
  Purchase #6 $233.60   8.392%   $253.2037   $253.20   $253.20   $253.20  
  Purchase #7 $51.93   6.527%   $55.3195   $55.32   $55.30   $55.30  
  7 purchase totals = $935.92       $1,013.9059   $1,013.90   $1,013.85   $1,014.00