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 $217.32   7.522%   $233.6668   $233.67   $233.65   $233.70  
  Purchase #2 $39.64   8.547%   $43.028   $43.03   $43.05   $43.00  
  Purchase #3 $23.47   9.142%   $25.6156   $25.62   $25.60   $25.60  
  Purchase #4 $34.81   3.169%   $35.9131   $35.91   $35.90   $35.90  
  Purchase #5 $236.77   11.643%   $264.3371   $264.34   $264.35   $264.30  
  Purchase #6 $150.41   6.713%   $160.507   $160.51   $160.50   $160.50  
  Purchase #7 $216.62   5.866%   $229.3269   $229.33   $229.35   $229.30  
  7 purchase totals = $919.04       $992.3945   $992.41   $992.40   $992.30