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 $54.70   8.220%   $59.1963   $59.20   $59.20   $59.20  
  Purchase #2 $235.81   6.117%   $250.2345   $250.23   $250.25   $250.20  
  Purchase #3 $159.90   13.177%   $180.97   $180.97   $180.95   $181.00  
  Purchase #4 $35.69   12.759%   $40.2437   $40.24   $40.25   $40.20  
  Purchase #5 $115.87   10.542%   $128.085   $128.09   $128.10   $128.10  
  Purchase #6 $203.33   11.677%   $227.0728   $227.07   $227.05   $227.10  
  Purchase #7 $153.41   10.156%   $168.9903   $168.99   $169.00   $169.00  
  7 purchase totals = $958.71       $1,054.7926   $1,054.79   $1,054.80   $1,054.80