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 $243.79   13.123%   $275.7826   $275.78   $275.80   $275.80  
  Purchase #2 $27.80   5.737%   $29.3949   $29.39   $29.40   $29.40  
  Purchase #3 $102.57   10.773%   $113.6199   $113.62   $113.60   $113.60  
  Purchase #4 $139.43   10.290%   $153.7773   $153.78   $153.80   $153.80  
  Purchase #5 $149.53   10.128%   $164.6744   $164.67   $164.65   $164.70  
  Purchase #6 $149.73   9.521%   $163.9858   $163.99   $164.00   $164.00  
  Purchase #7 $146.42   8.357%   $158.6563   $158.66   $158.65   $158.70  
  7 purchase totals = $959.27       $1,059.8912   $1,059.89   $1,059.90   $1,060.00