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 $248.52   8.363%   $269.3037   $269.30   $269.30   $269.30  
  Purchase #2 $194.44   11.365%   $216.5381   $216.54   $216.55   $216.50  
  Purchase #3 $43.77   9.487%   $47.9225   $47.92   $47.90   $47.90  
  Purchase #4 $54.81   11.159%   $60.9262   $60.93   $60.95   $60.90  
  Purchase #5 $75.70   8.604%   $82.2132   $82.21   $82.20   $82.20  
  Purchase #6 $120.52   10.841%   $133.5856   $133.59   $133.60   $133.60  
  Purchase #7 $170.88   8.445%   $185.3108   $185.31   $185.30   $185.30  
  7 purchase totals = $908.64       $995.8001   $995.80   $995.80   $995.70