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 $173.97   3.586%   $180.2086   $180.21   $180.20   $180.20  
  Purchase #2 $77.78   3.406%   $80.4292   $80.43   $80.45   $80.40  
  Purchase #3 $115.79   9.113%   $126.3419   $126.34   $126.35   $126.30  
  Purchase #4 $48.65   7.764%   $52.4272   $52.43   $52.45   $52.40  
  Purchase #5 $143.46   7.615%   $154.3845   $154.38   $154.40   $154.40  
  Purchase #6 $239.54   3.331%   $247.5191   $247.52   $247.50   $247.50  
  Purchase #7 $125.68   8.625%   $136.5199   $136.52   $136.50   $136.50  
  7 purchase totals = $924.87       $977.8304   $977.83   $977.85   $977.70