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 $173.83   13.575%   $197.4274   $197.43   $197.45   $197.40  
  Purchase #2 $105.89   3.431%   $109.5231   $109.52   $109.50   $109.50  
  Purchase #3 $20.96   13.129%   $23.7118   $23.71   $23.70   $23.70  
  Purchase #4 $93.26   4.523%   $97.4781   $97.48   $97.50   $97.50  
  Purchase #5 $132.77   9.771%   $145.743   $145.74   $145.75   $145.70  
  Purchase #6 $11.66   6.196%   $12.3825   $12.38   $12.40   $12.40  
  Purchase #7 $153.43   9.854%   $168.549   $168.55   $168.55   $168.50  
  7 purchase totals = $691.80       $754.8149   $754.81   $754.85   $754.70