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 $208.62   8.214%   $225.756   $225.76   $225.75   $225.80  
  Purchase #2 $238.70   5.690%   $252.282   $252.28   $252.30   $252.30  
  Purchase #3 $80.27   9.119%   $87.5898   $87.59   $87.60   $87.60  
  Purchase #4 $202.90   10.861%   $224.937   $224.94   $224.95   $224.90  
  Purchase #5 $149.52   10.799%   $165.6667   $165.67   $165.65   $165.70  
  Purchase #6 $126.54   12.752%   $142.6764   $142.68   $142.70   $142.70  
  Purchase #7 $26.80   12.606%   $30.1784   $30.18   $30.20   $30.20  
  7 purchase totals = $1,033.35       $1,129.0863   $1,129.10   $1,129.15   $1,129.20