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 $177.79   8.542%   $192.9768   $192.98   $193.00   $193.00  
  Purchase #2 $191.79   10.424%   $211.7822   $211.78   $211.80   $211.80  
  Purchase #3 $177.77   12.790%   $200.5068   $200.51   $200.50   $200.50  
  Purchase #4 $93.47   5.182%   $98.3136   $98.31   $98.30   $98.30  
  Purchase #5 $247.55   5.691%   $261.6381   $261.64   $261.65   $261.60  
  Purchase #6 $171.75   11.386%   $191.3055   $191.31   $191.30   $191.30  
  Purchase #7 $185.28   8.417%   $200.875   $200.88   $200.90   $200.90  
  7 purchase totals = $1,245.40       $1,357.3980   $1,357.41   $1,357.45   $1,357.40