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 $217.65   10.505%   $240.5141   $240.51   $240.50   $240.50  
  Purchase #2 $118.95   3.382%   $122.9729   $122.97   $122.95   $123.00  
  Purchase #3 $53.72   6.367%   $57.1404   $57.14   $57.15   $57.10  
  Purchase #4 $193.28   7.433%   $207.6465   $207.65   $207.65   $207.60  
  Purchase #5 $47.62   11.668%   $53.1763   $53.18   $53.20   $53.20  
  Purchase #6 $85.91   5.365%   $90.5191   $90.52   $90.50   $90.50  
  Purchase #7 $225.60   7.590%   $242.723   $242.72   $242.70   $242.70  
  7 purchase totals = $942.73       $1,014.6923   $1,014.69   $1,014.65   $1,014.60