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 $24.62   11.150%   $27.3651   $27.37   $27.35   $27.40  
  Purchase #2 $216.92   5.769%   $229.4341   $229.43   $229.45   $229.40  
  Purchase #3 $231.77   11.700%   $258.8871   $258.89   $258.90   $258.90  
  Purchase #4 $210.94   10.200%   $232.4559   $232.46   $232.45   $232.50  
  Purchase #5 $12.49   7.550%   $13.433   $13.43   $13.45   $13.40  
  Purchase #6 $67.43   4.852%   $70.7017   $70.70   $70.70   $70.70  
  Purchase #7 $165.57   6.352%   $176.087   $176.09   $176.10   $176.10  
  7 purchase totals = $929.74       $1,008.3639   $1,008.37   $1,008.40   $1,008.40