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 $177.77   5.764%   $188.0167   $188.02   $188.00   $188.00  
  Purchase #2 $117.67   12.729%   $132.6482   $132.65   $132.65   $132.60  
  Purchase #3 $186.76   11.406%   $208.0618   $208.06   $208.05   $208.10  
  Purchase #4 $112.79   11.850%   $126.1556   $126.16   $126.15   $126.20  
  Purchase #5 $179.91   12.263%   $201.9724   $201.97   $201.95   $202.00  
  Purchase #6 $72.33   4.680%   $75.715   $75.72   $75.70   $75.70  
  Purchase #7 $116.94   3.734%   $121.3065   $121.31   $121.30   $121.30  
  7 purchase totals = $964.17       $1,053.8762   $1,053.89   $1,053.80   $1,053.90