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 $137.77   3.171%   $142.1387   $142.14   $142.15   $142.10  
  Purchase #2 $207.34   6.102%   $219.9919   $219.99   $220.00   $220.00  
  Purchase #3 $209.91   9.191%   $229.2028   $229.20   $229.20   $229.20  
  Purchase #4 $101.76   6.615%   $108.4914   $108.49   $108.50   $108.50  
  Purchase #5 $134.47   3.256%   $138.8483   $138.85   $138.85   $138.80  
  Purchase #6 $86.81   3.319%   $89.6912   $89.69   $89.70   $89.70  
  Purchase #7 $121.97   12.669%   $137.4224   $137.42   $137.40   $137.40  
  7 purchase totals = $1,000.03       $1,065.7867   $1,065.78   $1,065.80   $1,065.70