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 $42.44   12.126%   $47.5863   $47.59   $47.60   $47.60  
  Purchase #2 $78.78   11.633%   $87.9445   $87.94   $87.95   $87.90  
  Purchase #3 $145.63   4.563%   $152.2751   $152.28   $152.30   $152.30  
  Purchase #4 $59.77   3.225%   $61.6976   $61.70   $61.70   $61.70  
  Purchase #5 $165.78   5.166%   $174.3442   $174.34   $174.35   $174.30  
  Purchase #6 $176.51   13.868%   $200.9884   $200.99   $201.00   $201.00  
  Purchase #7 $204.30   13.509%   $231.8989   $231.90   $231.90   $231.90  
  7 purchase totals = $873.21       $956.7350   $956.74   $956.80   $956.70