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 $56.96   7.433%   $61.1938   $61.19   $61.20   $61.20  
  Purchase #2 $61.48   11.326%   $68.4432   $68.44   $68.45   $68.40  
  Purchase #3 $42.36   12.287%   $47.5648   $47.56   $47.55   $47.60  
  Purchase #4 $170.46   5.403%   $179.67   $179.67   $179.65   $179.70  
  Purchase #5 $107.44   12.386%   $120.7475   $120.75   $120.75   $120.70  
  Purchase #6 $236.94   6.530%   $252.4122   $252.41   $252.40   $252.40  
  Purchase #7 $201.82   3.452%   $208.7868   $208.79   $208.80   $208.80  
  7 purchase totals = $877.46       $938.8183   $938.81   $938.80   $938.80