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 $92.51   4.589%   $96.7553   $96.76   $96.75   $96.80  
  Purchase #2 $50.88   11.606%   $56.7851   $56.79   $56.80   $56.80  
  Purchase #3 $170.83   3.260%   $176.3991   $176.40   $176.40   $176.40  
  Purchase #4 $157.92   4.575%   $165.1448   $165.14   $165.15   $165.10  
  Purchase #5 $243.50   13.487%   $276.3408   $276.34   $276.35   $276.30  
  Purchase #6 $6.71   8.614%   $7.288   $7.29   $7.30   $7.30  
  Purchase #7 $60.62   8.626%   $65.8491   $65.85   $65.85   $65.80  
  7 purchase totals = $782.97       $844.5622   $844.57   $844.60   $844.50