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 $232.62   6.311%   $247.3006   $247.30   $247.30   $247.30  
  Purchase #2 $70.98   4.763%   $74.3608   $74.36   $74.35   $74.40  
  Purchase #3 $34.96   8.785%   $38.0312   $38.03   $38.05   $38.00  
  Purchase #4 $235.69   11.769%   $263.4284   $263.43   $263.45   $263.40  
  Purchase #5 $164.62   8.324%   $178.323   $178.32   $178.30   $178.30  
  Purchase #6 $208.30   10.125%   $229.3904   $229.39   $229.40   $229.40  
  Purchase #7 $8.58   6.138%   $9.1066   $9.11   $9.10   $9.10  
  7 purchase totals = $955.75       $1,039.9410   $1,039.94   $1,039.95   $1,039.90