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 $46.29   8.751%   $50.3408   $50.34   $50.35   $50.30  
  Purchase #2 $220.50   9.749%   $241.9965   $242.00   $242.00   $242.00  
  Purchase #3 $243.52   6.413%   $259.1369   $259.14   $259.15   $259.10  
  Purchase #4 $134.85   10.706%   $149.287   $149.29   $149.30   $149.30  
  Purchase #5 $248.25   4.862%   $260.3199   $260.32   $260.30   $260.30  
  Purchase #6 $246.66   11.857%   $275.9065   $275.91   $275.90   $275.90  
  Purchase #7 $187.81   5.517%   $198.1715   $198.17   $198.15   $198.20  
  7 purchase totals = $1,327.88       $1,435.1591   $1,435.17   $1,435.15   $1,435.10