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 $65.29   13.462%   $74.0793   $74.08   $74.10   $74.10  
  Purchase #2 $192.32   8.178%   $208.0479   $208.05   $208.05   $208.00  
  Purchase #3 $238.51   4.855%   $250.0897   $250.09   $250.10   $250.10  
  Purchase #4 $74.63   11.305%   $83.0669   $83.07   $83.05   $83.10  
  Purchase #5 $237.68   11.478%   $264.9609   $264.96   $264.95   $265.00  
  Purchase #6 $157.59   4.465%   $164.6264   $164.63   $164.65   $164.60  
  Purchase #7 $12.55   4.354%   $13.0964   $13.10   $13.10   $13.10  
  7 purchase totals = $978.57       $1,057.9675   $1,057.98   $1,058.00   $1,058.00