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 $69.73   6.589%   $74.3245   $74.32   $74.30   $74.30  
  Purchase #2 $186.89   11.317%   $208.0403   $208.04   $208.05   $208.00  
  Purchase #3 $73.46   9.440%   $80.3946   $80.39   $80.40   $80.40  
  Purchase #4 $236.38   4.286%   $246.5112   $246.51   $246.50   $246.50  
  Purchase #5 $30.65   13.357%   $34.7439   $34.74   $34.75   $34.70  
  Purchase #6 $51.64   12.681%   $58.1885   $58.19   $58.20   $58.20  
  Purchase #7 $241.85   8.748%   $263.007   $263.01   $263.00   $263.00  
  7 purchase totals = $890.60       $965.2100   $965.20   $965.20   $965.10