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 $206.75   9.288%   $225.9529   $225.95   $225.95   $226.00  
  Purchase #2 $179.30   3.368%   $185.3388   $185.34   $185.35   $185.30  
  Purchase #3 $242.85   13.864%   $276.5187   $276.52   $276.50   $276.50  
  Purchase #4 $246.47   3.277%   $254.5468   $254.55   $254.55   $254.50  
  Purchase #5 $241.90   5.871%   $256.1019   $256.10   $256.10   $256.10  
  Purchase #6 $193.65   5.246%   $203.8089   $203.81   $203.80   $203.80  
  Purchase #7 $163.62   6.226%   $173.807   $173.81   $173.80   $173.80  
  7 purchase totals = $1,474.54       $1,576.0750   $1,576.08   $1,576.05   $1,576.00