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 $23.71   10.777%   $26.2652   $26.27   $26.25   $26.30  
  Purchase #2 $177.88   10.829%   $197.1426   $197.14   $197.15   $197.10  
  Purchase #3 $238.52   10.161%   $262.756   $262.76   $262.75   $262.80  
  Purchase #4 $196.31   10.588%   $217.0953   $217.10   $217.10   $217.10  
  Purchase #5 $79.65   10.411%   $87.9424   $87.94   $87.95   $87.90  
  Purchase #6 $54.33   5.736%   $57.4464   $57.45   $57.45   $57.40  
  Purchase #7 $44.82   6.395%   $47.6862   $47.69   $47.70   $47.70  
  7 purchase totals = $815.22       $896.3341   $896.35   $896.35   $896.30