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 $126.88   11.786%   $141.8341   $141.83   $141.85   $141.80  
  Purchase #2 $186.54   12.293%   $209.4714   $209.47   $209.45   $209.50  
  Purchase #3 $147.96   5.235%   $155.7057   $155.71   $155.70   $155.70  
  Purchase #4 $114.39   6.809%   $122.1788   $122.18   $122.20   $122.20  
  Purchase #5 $47.81   7.854%   $51.565   $51.57   $51.55   $51.60  
  Purchase #6 $120.34   7.797%   $129.7229   $129.72   $129.70   $129.70  
  Purchase #7 $153.98   12.787%   $173.6694   $173.67   $173.65   $173.70  
  7 purchase totals = $897.90       $984.1473   $984.15   $984.10   $984.20