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 $239.65   11.126%   $266.3135   $266.31   $266.30   $266.30  
  Purchase #2 $50.70   9.689%   $55.6123   $55.61   $55.60   $55.60  
  Purchase #3 $113.94   11.318%   $126.8357   $126.84   $126.85   $126.80  
  Purchase #4 $250.79   9.622%   $274.921   $274.92   $274.90   $274.90  
  Purchase #5 $172.82   6.469%   $183.9997   $184.00   $184.00   $184.00  
  Purchase #6 $76.98   4.823%   $80.6927   $80.69   $80.70   $80.70  
  Purchase #7 $207.33   9.404%   $226.8273   $226.83   $226.85   $226.80  
  7 purchase totals = $1,112.21       $1,215.2022   $1,215.20   $1,215.20   $1,215.10