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 $41.71   3.117%   $43.0101   $43.01   $43.00   $43.00  
  Purchase #2 $239.36   3.531%   $247.8118   $247.81   $247.80   $247.80  
  Purchase #3 $116.52   11.658%   $130.1039   $130.10   $130.10   $130.10  
  Purchase #4 $231.39   5.676%   $244.5237   $244.52   $244.50   $244.50  
  Purchase #5 $122.25   5.305%   $128.7354   $128.74   $128.75   $128.70  
  Purchase #6 $95.48   10.617%   $105.6171   $105.62   $105.60   $105.60  
  Purchase #7 $38.60   12.395%   $43.3845   $43.38   $43.40   $43.40  
  7 purchase totals = $885.31       $943.1865   $943.18   $943.15   $943.10