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 $76.59   6.420%   $81.5071   $81.51   $81.50   $81.50  
  Purchase #2 $201.86   8.797%   $219.6176   $219.62   $219.60   $219.60  
  Purchase #3 $246.77   13.812%   $280.8539   $280.85   $280.85   $280.90  
  Purchase #4 $224.95   13.135%   $254.4972   $254.50   $254.50   $254.50  
  Purchase #5 $98.78   12.352%   $110.9813   $110.98   $111.00   $111.00  
  Purchase #6 $152.37   6.103%   $161.6691   $161.67   $161.65   $161.70  
  Purchase #7 $49.97   7.703%   $53.8192   $53.82   $53.80   $53.80  
  7 purchase totals = $1,051.29       $1,162.9454   $1,162.95   $1,162.90   $1,163.00