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 $244.72   12.199%   $274.5734   $274.57   $274.55   $274.60  
  Purchase #2 $242.88   3.615%   $251.6601   $251.66   $251.65   $251.70  
  Purchase #3 $46.63   9.840%   $51.2184   $51.22   $51.20   $51.20  
  Purchase #4 $200.92   5.438%   $211.846   $211.85   $211.85   $211.80  
  Purchase #5 $226.50   6.681%   $241.6325   $241.63   $241.65   $241.60  
  Purchase #6 $82.51   13.637%   $93.7619   $93.76   $93.75   $93.80  
  Purchase #7 $81.80   4.584%   $85.5497   $85.55   $85.55   $85.50  
  7 purchase totals = $1,125.96       $1,210.2420   $1,210.24   $1,210.20   $1,210.20