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 $180.77   7.611%   $194.5284   $194.53   $194.55   $194.50  
  Purchase #2 $231.99   12.468%   $260.9145   $260.91   $260.90   $260.90  
  Purchase #3 $69.30   8.681%   $75.3159   $75.32   $75.30   $75.30  
  Purchase #4 $242.88   8.570%   $263.6948   $263.69   $263.70   $263.70  
  Purchase #5 $177.29   7.659%   $190.8686   $190.87   $190.85   $190.90  
  Purchase #6 $136.48   11.685%   $152.4277   $152.43   $152.45   $152.40  
  Purchase #7 $24.55   5.167%   $25.8185   $25.82   $25.80   $25.80  
  7 purchase totals = $1,063.26       $1,163.5684   $1,163.57   $1,163.55   $1,163.50