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 $174.66   8.758%   $189.9567   $189.96   $189.95   $190.00  
  Purchase #2 $246.65   11.671%   $275.4365   $275.44   $275.45   $275.40  
  Purchase #3 $226.45   13.439%   $256.8826   $256.88   $256.90   $256.90  
  Purchase #4 $117.41   6.358%   $124.8749   $124.87   $124.85   $124.90  
  Purchase #5 $142.94   12.403%   $160.6688   $160.67   $160.65   $160.70  
  Purchase #6 $222.36   8.871%   $242.0856   $242.09   $242.10   $242.10  
  Purchase #7 $10.94   7.387%   $11.7481   $11.75   $11.75   $11.70  
  7 purchase totals = $1,141.41       $1,261.6532   $1,261.66   $1,261.65   $1,261.70