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 $55.76   7.446%   $59.9119   $59.91   $59.90   $59.90  
  Purchase #2 $136.38   9.814%   $149.7643   $149.76   $149.75   $149.80  
  Purchase #3 $154.47   13.254%   $174.9435   $174.94   $174.95   $174.90  
  Purchase #4 $236.53   4.265%   $246.618   $246.62   $246.60   $246.60  
  Purchase #5 $237.64   7.160%   $254.655   $254.66   $254.65   $254.70  
  Purchase #6 $50.88   3.834%   $52.8307   $52.83   $52.85   $52.80  
  Purchase #7 $151.27   3.450%   $156.4888   $156.49   $156.50   $156.50  
  7 purchase totals = $1,022.93       $1,095.2122   $1,095.21   $1,095.20   $1,095.20