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 $244.62   6.594%   $260.7502   $260.75   $260.75   $260.80  
  Purchase #2 $217.86   10.406%   $240.5305   $240.53   $240.55   $240.50  
  Purchase #3 $106.51   4.579%   $111.3871   $111.39   $111.40   $111.40  
  Purchase #4 $171.96   9.841%   $188.8826   $188.88   $188.90   $188.90  
  Purchase #5 $25.85   11.565%   $28.8396   $28.84   $28.85   $28.80  
  Purchase #6 $8.98   7.296%   $9.6352   $9.64   $9.65   $9.60  
  Purchase #7 $216.47   5.803%   $229.0318   $229.03   $229.05   $229.00  
  7 purchase totals = $992.25       $1,069.0570   $1,069.06   $1,069.15   $1,069.00