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 $225.36   12.821%   $254.2534   $254.25   $254.25   $254.30  
  Purchase #2 $226.52   7.126%   $242.6618   $242.66   $242.65   $242.70  
  Purchase #3 $41.53   7.874%   $44.8001   $44.80   $44.80   $44.80  
  Purchase #4 $156.83   3.848%   $162.8648   $162.86   $162.85   $162.90  
  Purchase #5 $193.66   5.145%   $203.6238   $203.62   $203.60   $203.60  
  Purchase #6 $39.38   10.206%   $43.3991   $43.40   $43.40   $43.40  
  Purchase #7 $192.78   10.596%   $213.207   $213.21   $213.20   $213.20  
  7 purchase totals = $1,076.06       $1,164.8100   $1,164.80   $1,164.75   $1,164.90