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 $161.34   10.854%   $178.8518   $178.85   $178.85   $178.90  
  Purchase #2 $180.82   10.434%   $199.6868   $199.69   $199.70   $199.70  
  Purchase #3 $128.25   12.107%   $143.7772   $143.78   $143.80   $143.80  
  Purchase #4 $246.55   4.316%   $257.1911   $257.19   $257.20   $257.20  
  Purchase #5 $64.80   9.193%   $70.7571   $70.76   $70.75   $70.80  
  Purchase #6 $179.81   9.773%   $197.3828   $197.38   $197.40   $197.40  
  Purchase #7 $5.89   7.777%   $6.3481   $6.35   $6.35   $6.30  
  7 purchase totals = $967.46       $1,053.9949   $1,054.00   $1,054.05   $1,054.10