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 $137.81   10.753%   $152.6287   $152.63   $152.65   $152.60  
  Purchase #2 $32.88   4.334%   $34.305   $34.31   $34.30   $34.30  
  Purchase #3 $43.33   12.835%   $48.8914   $48.89   $48.90   $48.90  
  Purchase #4 $106.81   9.453%   $116.9067   $116.91   $116.90   $116.90  
  Purchase #5 $241.88   11.505%   $269.7083   $269.71   $269.70   $269.70  
  Purchase #6 $190.98   8.642%   $207.4845   $207.48   $207.50   $207.50  
  Purchase #7 $150.99   12.676%   $170.1295   $170.13   $170.15   $170.10  
  7 purchase totals = $904.68       $1,000.0541   $1,000.06   $1,000.10   $1,000.00