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 $38.92   6.696%   $41.5261   $41.53   $41.55   $41.50  
  Purchase #2 $115.42   7.513%   $124.0915   $124.09   $124.10   $124.10  
  Purchase #3 $22.65   11.699%   $25.2998   $25.30   $25.30   $25.30  
  Purchase #4 $212.51   10.752%   $235.3591   $235.36   $235.35   $235.40  
  Purchase #5 $151.45   7.689%   $163.095   $163.10   $163.10   $163.10  
  Purchase #6 $140.30   5.312%   $147.7527   $147.75   $147.75   $147.80  
  Purchase #7 $218.36   3.500%   $226.0026   $226.00   $226.00   $226.00  
  7 purchase totals = $899.61       $963.1268   $963.13   $963.15   $963.20