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 $70.41   3.815%   $73.0961   $73.10   $73.10   $73.10  
  Purchase #2 $113.56   8.272%   $122.9537   $122.95   $122.95   $123.00  
  Purchase #3 $48.53   11.515%   $54.1182   $54.12   $54.10   $54.10  
  Purchase #4 $210.42   8.542%   $228.3941   $228.39   $228.40   $228.40  
  Purchase #5 $109.69   5.615%   $115.8491   $115.85   $115.85   $115.80  
  Purchase #6 $201.72   10.238%   $222.3721   $222.37   $222.35   $222.40  
  Purchase #7 $163.90   6.317%   $174.2536   $174.25   $174.25   $174.30  
  7 purchase totals = $918.23       $991.0369   $991.03   $991.00   $991.10