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 $216.72   11.715%   $242.1087   $242.11   $242.10   $242.10  
  Purchase #2 $53.78   12.406%   $60.4519   $60.45   $60.45   $60.50  
  Purchase #3 $116.79   3.613%   $121.0096   $121.01   $121.00   $121.00  
  Purchase #4 $41.36   10.366%   $45.6474   $45.65   $45.65   $45.60  
  Purchase #5 $163.78   8.767%   $178.1386   $178.14   $178.15   $178.10  
  Purchase #6 $247.69   4.490%   $258.8113   $258.81   $258.80   $258.80  
  Purchase #7 $240.50   6.104%   $255.1801   $255.18   $255.20   $255.20  
  7 purchase totals = $1,080.62       $1,161.3476   $1,161.35   $1,161.35   $1,161.30