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 $145.47   6.287%   $154.6157   $154.62   $154.60   $154.60  
  Purchase #2 $75.89   12.411%   $85.3087   $85.31   $85.30   $85.30  
  Purchase #3 $25.45   6.665%   $27.1462   $27.15   $27.15   $27.10  
  Purchase #4 $200.71   9.423%   $219.6229   $219.62   $219.60   $219.60  
  Purchase #5 $227.50   4.459%   $237.6442   $237.64   $237.65   $237.60  
  Purchase #6 $207.43   8.865%   $225.8187   $225.82   $225.80   $225.80  
  Purchase #7 $8.61   9.238%   $9.4054   $9.41   $9.40   $9.40  
  7 purchase totals = $891.06       $959.5618   $959.57   $959.50   $959.40