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 $68.61   12.724%   $77.3399   $77.34   $77.35   $77.30  
  Purchase #2 $38.41   13.420%   $43.5646   $43.56   $43.55   $43.60  
  Purchase #3 $243.30   3.720%   $252.3508   $252.35   $252.35   $252.40  
  Purchase #4 $116.66   3.824%   $121.1211   $121.12   $121.10   $121.10  
  Purchase #5 $194.87   10.108%   $214.5675   $214.57   $214.55   $214.60  
  Purchase #6 $45.94   3.378%   $47.4919   $47.49   $47.50   $47.50  
  Purchase #7 $245.82   11.322%   $273.6517   $273.65   $273.65   $273.70  
  7 purchase totals = $953.61       $1,030.0875   $1,030.08   $1,030.05   $1,030.20